Series route: This guide belongs to the complete PSLE Learner’s Guide volume directory. The original PSLE Learning Guide supplies the wider English, Mathematics and Science route, while PSLE English, PSLE Mathematics, PSLE Science provide verified subject-specific continuation.
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This volume solves one precise learner problem: the learner treats approximately as decorative, records a rounded value with an exact equals sign, or rejects a sensible estimate because it does not match an unrounded result digit for digit. The aim is not to memorise a slogan. It is to understand the mechanism well enough to recognise the idea when the wording, numbers, diagram or context changes. A Primary 6 learner should be able to explain the decision, perform it under time pressure, and detect a tempting answer that only looks familiar.
- Understand the mechanism before memorising a form.
- Study the worked examples and compare near-misses.
- Repair common misconceptions with targeted tests.
- Complete graded independent practice before reading the answers.
- Use delayed transfer and examination control to make the skill durable.
- Use the parent and tutor notes only after the learner has attempted the work.
The problem beneath the mistake
The exact result 19.84 can be approximately 20 when rounded to the nearest whole number.
The same result is approximately 19.8 to one decimal place. Approximation is incomplete unless the relevant precision is understood.
An estimate of 398×51 may use 400×50=20,000. The purpose is a quick magnitude check, not a replacement for an exact product when exactness is required.
A measured length of about 12 cm may reflect instrument resolution or reading uncertainty. The object does not become exactly 12 cm because the answer is convenient.
In English, words such as about, roughly, nearly and approximately differ slightly in tone and direction. Nearly 50 usually suggests below 50, while approximately 50 can lie on either side.
In Mathematics, the symbol ≈ distinguishes approximate equality from exact equality =.
In Science, observations and measurements should not claim more precision than the apparatus or method supports.
A graph reading between grid lines may be estimated, while a value printed in a table can be exact within the problem’s stated model.
Rounding during intermediate steps can change the final answer. Keep exact or fuller values until the requested final stage when possible.
An approximate answer still needs units. “About 5” is incomplete if the quantity could be seconds, metres or pupils.
Tolerance matters. Approximately 100 may be acceptable to the nearest ten but poor to the nearest one.
The safe routine is identify exact or measured source, choose precision, calculate with guard digits, round once, attach units and label the result as approximate.
Core decision: “Approximately” tells the reader that a value is close to, but not claimed to be exactly equal to, a target value at the stated or implied precision. Identify whether the approximation comes from rounding, estimation, measurement limits or simplified modelling. Preserve the unit, state the precision where needed, and use words or notation that do not turn a qualified claim into exact equality.
A useful rule has three parts: a trigger, an operation and a check. The trigger tells you when the rule applies. The operation tells you what to do. The check tells you whether the result still matches the meaning of the question. Learners who remember only the operation often apply it in the wrong place; learners who remember only an example often freeze when the surface details change.
Mechanism: why the rule works
1. Find the source of approximation
Rounding, estimation, measurement and modelling create different kinds of closeness.
Diagnostic question: Why is the value not exact? Reliable response: Name the source before judging accuracy.
2. Identify the precision
Nearest whole, nearest ten, decimal places and significant figures define different targets.
Diagnostic question: To what place or resolution is the value reported? Reliable response: State the precision when the task supplies it.
3. Protect exact equality
The equals sign claims the two expressions have the same value, while approximately equal allows a controlled difference.
Diagnostic question: Is any information discarded or estimated? Reliable response: Use ≈ or words such as approximately after approximation.
4. Keep guard digits
Rounding every intermediate value compounds error.
Diagnostic question: Can the exact fraction or fuller decimal be retained? Reliable response: Round at the final requested stage unless instructed otherwise.
5. Preserve quantity and unit
Approximation changes precision, not the kind of quantity measured.
Diagnostic question: What does the number measure? Reliable response: Carry the unit and referent into the approximate statement.
6. Check reasonableness
An approximation should be close enough for its purpose and consistent with bounds.
Diagnostic question: Could the exact value plausibly round to the reported result? Reliable response: Use lower and upper rounding intervals or an estimate check.
Worked examples: make the decision visible
Do not race through these examples. Before reading each explanation, name the evidence that matters and the information that does not. Then compare the correct route with the tempting route. That comparison is where the transferable learning sits.
Worked example 1: Nearest whole
Task. Round 19.84 to the nearest whole number.
Reasoning. The tenths digit is 8, so 19 rounds up. The controlling idea is the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. 19.84≈20.
Independent check. The exact value lies between 19.5 and 20.5. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 2: Nearest ten
Task. A crowd count is 347; report approximately to the nearest ten.
Reasoning. The ones digit is 7. The controlling idea is the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Approximately 350 people.
Independent check. The unit and people referent remain. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 3: Product estimate
Task. Estimate 398×51.
Reasoning. Round to compatible convenient numbers 400 and 50. The controlling idea is the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Approximately 20,000.
Independent check. The exact product should be near this magnitude. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 4: Measured length
Task. A ruler reading lies slightly above 12.3 cm.
Reasoning. The apparatus and reading limit precision. The controlling idea is the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Report approximately 12.3 cm at the justified resolution.
Independent check. Do not invent extra decimal places. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 5: Graph interpolation
Task. A point lies halfway between 6 and 8 on a coarse axis.
Reasoning. The position supports an estimated reading near 7. The controlling idea is the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. The value is approximately 7 units.
Independent check. Check the axis scale and unit. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 6: Nearly versus approximately
Task. A tank contains 49.8 L.
Reasoning. Approximately 50 L is neutral closeness; nearly 50 L suggests it is just below 50. The controlling idea is the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Both may fit, but the second carries directional nuance.
Independent check. Compare with 50.2 L. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 7: Intermediate rounding
Task. Compute 10÷3×6.
Reasoning. Keeping 10/3 gives exactly 20; using 3.3 early gives 19.8. The controlling idea is the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Retain the fraction until the end.
Independent check. Reverse with multiplication. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 8: False exact sign
Task. A learner writes 1/3=0.33.
Reasoning. 0.33 is a rounded truncation, not the exact recurring decimal. The controlling idea is the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Write 1/3≈0.33 to two decimal places.
Independent check. Multiply 0.33 by 3 to see 0.99. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Deepening lab: compare cases, conditions and limits
A method becomes independent when you can say where it applies, where it stops and which change would alter the conclusion. The cases below deliberately vary one structural feature at a time. For each case, pause before the analysis and predict whether the core rule remains available. Then name the exact condition that controls the decision. This is harder than repeating a worked solution, but it is also closer to what an unfamiliar examination item demands.
Deepening case 1: Exact integer
Case. 7+5=12.
Analysis. No approximation occurred. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Use exact equality. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 2: Rounded decimal
Case. π is represented as 3.14.
Analysis. Digits have been limited. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Use approximate language. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 3: Nearest hundred
Case. 2,649 becomes 2,600.
Analysis. Precision is hundreds. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. State the rounding interval. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 4: One decimal place
Case. 4.26 becomes 4.3.
Analysis. The hundredths digit controls the decision. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Check the place value. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 5: Measurement resolution
Case. A scale marks grams only.
Analysis. Reporting thousandths of a gram is unsupported. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Match precision to apparatus. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 6: Counted objects
Case. There are exactly 28 pupils present.
Analysis. A direct complete count can be exact in the task. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Do not weaken without reason. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 7: Estimated crowd
Case. A large crowd is assessed visually.
Analysis. The count may be approximate. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. State method limitations. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 8: Graph point on gridline
Case. A plotted point exactly meets a labelled line in the idealised graph.
Analysis. The problem may intend an exact reading. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Follow the model and labels. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 9: Graph point between lines
Case. Interpolation is needed.
Analysis. The reading is estimated. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Avoid false precision. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 10: About ten minutes
Case. Everyday speech allows flexible closeness.
Analysis. Purpose controls tolerance. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Clarify for a timetable. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 11: Nearly full
Case. The state is close to full but not full.
Analysis. Nearly often implies a direction. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Do not treat as exactly full. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 12: Roughly equal groups
Case. Group sizes are close but not proven identical.
Analysis. Roughly weakens exact equality. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Give actual counts if available. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 13: Upper bound
Case. A value rounding to 20 whole lies below 20.5.
Analysis. Bounds test plausibility. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Include the lower bound. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 14: Repeated rounding
Case. Several steps each round.
Analysis. Error can accumulate. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Keep guard digits. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 15: Calculator display
Case. Many digits appear.
Analysis. Display length does not guarantee meaningful precision. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Use requested accuracy. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 16: Unit conversion
Case. 2.54 cm equals exactly 1 inch by definition in suitable context.
Analysis. Not every decimal conversion is approximate. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Check whether conversion is defined or measured. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 17: Model assumption
Case. A shape is treated as a perfect circle.
Analysis. The calculation may be exact within the model but approximate for the real object. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Separate model from reality. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 18: Answer tolerance
Case. Two rounded results differ slightly.
Analysis. Both may be acceptable at a stated precision. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Compare intervals. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 19: Communication choice
Case. The symbol ≈ may be unfamiliar in prose.
Analysis. Words can state approximately clearly. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Match audience and format. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 20: Complete audit
Case. Source, exact value, precision, approximate value, unit and purpose are recorded.
Analysis. The claim is neither too strong nor too vague. Notice that the answer depends on the source of approximation, the chosen precision, the exact value being represented and the strength of the equality claim; changing a decorative detail would not be enough to change the reasoning.
Challenge. Perform a bounds check. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Finish the lab with a blank-page recall. Write the rule, its conditions, one confirming example, one near-miss and one independent check from memory. Compare that page with the article only after finishing. If the rule is correct but the condition is missing, the learning is not yet safe: an overgeneralised rule can produce confident errors. If the condition is correct but no example can be generated, practise construction rather than rereading.
Common misconceptions and targeted repairs
Misconception 1: Approximately means exactly
What the learner may think. The qualifier can be ignored.
Why it fails. It explicitly weakens the equality claim to closeness. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Name the permitted precision or tolerance. Use this short test immediately: Would the values remain identical before rounding?
Misconception 2: Every decimal is approximate
What the learner may think. A decimal point proves estimation.
Why it fails. Terminating decimals can be exact, and fractions can be approximate when rounded. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Ask how the value was obtained. Use this short test immediately: Was information discarded?
Misconception 3: More digits are always better
What the learner may think. A calculator gives eight digits, so write all eight.
Why it fails. Unjustified digits create false precision. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Match the task and measurement resolution. Use this short test immediately: Which digits are supported?
Misconception 4: Units can be dropped
What the learner may think. Approximate numbers need no unit.
Why it fails. The quantity type remains essential. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Carry the unit through rounding. Use this short test immediately: Approximately five what?
Misconception 5: Round at every line
What the learner may think. Frequent rounding makes work easier and harmless.
Why it fails. Errors can accumulate and change the final rounded answer. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Keep exact forms or guard digits. Use this short test immediately: Can you round once at the end?
Misconception 6: Estimate must match exact digits
What the learner may think. An estimate is wrong unless it equals the exact calculation.
Why it fails. Its job is to give a useful nearby magnitude. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Judge against purpose and bounds. Use this short test immediately: Is the estimate plausibly close?
Graded independent practice
Attempt each item without looking ahead. Write one line that identifies the controlling evidence before writing the final answer. Items 1–3 check recognition, 4–7 require explanation, and the later items change the surface form so that memory alone is insufficient.
Practice 1: Notation
Question. Write 2/3 rounded to 0.67.
Explained answer. 2/3≈0.67.
Why this answer earns trust. The finite decimal is not exactly the recurring fraction. Transfer variation: State two decimal places.
Practice 2: Exactness
Question. Should 8+4 use = or ≈ before 12?
Explained answer. = because the values are exactly equal.
Why this answer earns trust. No estimation or rounding occurred. Transfer variation: Explain the claim.
Practice 3: Nearest whole
Question. Round 7.62.
Explained answer. 8.
Why this answer earns trust. The value is at least 7.5 and below 8.5. Transfer variation: Write with ≈.
Practice 4: Nearest ten
Question. Round 463.
Explained answer. 460.
Why this answer earns trust. The ones digit is 3. Transfer variation: State the rounding interval.
Practice 5: Estimate
Question. Estimate 603×19.
Explained answer. About 12,000 using 600×20.
Why this answer earns trust. Convenient close factors give magnitude. Transfer variation: Compare with exact product.
Practice 6: Measurement
Question. A ruler has 1 mm markings. Should you report 12.345678 cm?
Explained answer. No.
Why this answer earns trust. The apparatus does not support that many digits. Transfer variation: Choose justified precision.
Practice 7: Language nuance
Question. What does nearly 100 suggest?
Explained answer. A value close to but generally below 100.
Why this answer earns trust. Nearly often carries directional meaning. Transfer variation: Contrast approximately 100.
Practice 8: Guard digits
Question. Why keep 1/3 instead of 0.3 in a multi-step calculation?
Explained answer. The fraction preserves the exact value and avoids large early rounding error.
Why this answer earns trust. 0.3 is a coarse approximation. Transfer variation: Calculate both routes.
Practice 9: Bounds
Question. What values round to 50 to the nearest whole?
Explained answer. Values from 49.5 up to but not including 50.5.
Why this answer earns trust. The interval checks plausibility. Transfer variation: Adapt to nearest ten.
Practice 10: Routine
Question. State the approximation routine.
Explained answer. Identify source and exact value, choose precision, retain guard digits, round once, use ≈ or qualifying words, attach units and check bounds.
Why this answer earns trust. It controls both calculation and claim strength. Transfer variation: Apply to a graph estimate.
Delayed transfer: prove that the learning lasts
Transfer test 1: Exact-or-approximate sort
Classify twenty statements from arithmetic, measurements, graphs and prose. Do this after a delay, without rereading the worked examples. The purpose is to test retrieval and decision-making, not immediate imitation.
Success criterion. Every classification names the source of exactness or approximation. If the criterion is not met, return to the smallest missing decision rather than repeating the entire chapter.
Transfer test 2: Precision ladder
Report one value to the nearest whole, tenth, hundredth and suitable measurement resolution. Do this after a delay, without rereading the worked examples. The purpose is to test retrieval and decision-making, not immediate imitation.
Success criterion. Each statement uses correct notation, unit and rounding interval. If the criterion is not met, return to the smallest missing decision rather than repeating the entire chapter.
Transfer test 3: Delayed error audit
After two days, repair a solution with early rounding, missing units and an exact equals sign. Do this after a delay, without rereading the worked examples. The purpose is to test retrieval and decision-making, not immediate imitation.
Success criterion. The revised solution retains guard digits and makes one justified approximate claim. If the criterion is not met, return to the smallest missing decision rather than repeating the entire chapter.
Examination control
1. Read the job before the story. Underline the command and the noun it governs. “Explain the change,” “state the word,” “find the fraction” and “identify the evidence” are different jobs even when the surrounding context is similar.
2. Separate given information from remembered information. Use only the facts supplied for the current task plus secure subject knowledge. Do not let a previous question, a familiar worksheet or an expected pattern silently become new evidence.
3. Write enough working to expose the decision. A marker or teacher should be able to see the relationship that justifies the answer. Extra sentences are not automatically stronger; the strongest working is concise, relevant and checkable.
4. Reserve a different-route check. For language, read the sentence for meaning and grammar. For mathematics, estimate or reverse the operation. For science, check the claim against the stated observation and a conservation or fair-test principle.
5. Stop when the requested job is complete. Unrequested speculation can contradict a correct answer. Add detail only when it explains the mechanism or satisfies another explicit part of the question.
Under time pressure, use a compact four-part margin routine: trigger → evidence → operation → check. Trigger names the feature that activates the method. Evidence identifies the exact words, values or observations allowed. Operation performs the language, mathematical or scientific step. Check asks whether the final statement answers the requested job, preserves units or referents, and avoids a stronger claim than the evidence supports.
A compact error log
After practice, do not record only “careless mistake.” Name the broken decision. Useful labels include trigger missed, evidence imported, relationship reversed, referent lost, unit dropped, operation correct but job wrong, and check repeated the same route. Add one prevention cue beside the label. A short accurate log is more useful than a long emotional account because it tells the learner what to do on the next item.
Review the log after two days and again after a week. Reattempt only one or two representative items first. If the method transfers, move to a mixed set. If it fails, repair the exact link between trigger and operation. This spacing matters because a solution can feel obvious while it is still visible and disappear when the page is closed.
Notes for parents and tutors
Ask “Approximate for what purpose and to what precision?” rather than accepting “about” as a complete explanation.
Use shopping estimates and ruler readings to contrast useful approximation with false exactness.
Encourage one final rounding step and a reasonableness check instead of repeatedly shortening calculator values.
The adult’s most useful question is not “Why were you careless?” but “Which decision did the evidence require?” Ask the learner to point to the controlling word, value, relationship or observation. If the learner can explain that link, reduce support. If the learner cannot, model one example and then change the surface details for the next attempt.
Frequently asked questions
Does approximately mean equal?
No. It means close at a stated or understood precision.
When should I use ≈?
Use it when a displayed value results from rounding, estimation or another approximation.
Can a decimal be exact?
Yes. For example, 0.5 is exactly one half.
Why keep extra digits during working?
They reduce accumulated rounding error before the final required answer.
Must an approximate answer have units?
Yes when it represents a measured or contextual quantity.
What is the fastest check?
Ask what was discarded, what precision is intended and whether the exact value lies in the rounding interval.
Next routes
Return to the complete volume directory to locate the series, use the original PSLE Learning Guide for the foundation route, and continue through PSLE English, PSLE Mathematics, PSLE Science for verified subject guidance. The next useful task is a mixed set in which this idea is sometimes relevant and sometimes irrelevant; that is the point at which a learner must choose, not merely copy.