A package has a mass of 2 kg 150 g, and 875 g of its contents are taken away. What remains? The answer is 1 kg 275 g. For families near Chiltern Park choosing weekday or weekend Primary 3 Mathematics tuition, the real diagnostic is whether the learner can preserve the meaning of kilograms and grams through subtraction.
A reliable route converts the starting amount to 2,150 g, subtracts 875 g to get 1,275 g, then expresses that remainder as one kilogram and 275 grams. A learner who writes 2 kg 725 g may have reversed the gram subtraction or failed to make the needed exchange.
Singapore’s current Primary 3 syllabus includes compound units of mass and conversion between kilograms and grams. A good tutor should connect the written working to a mass bar, check with addition, then ask for an independent unseen question after the lesson.
Find the next useful step
The answer is 1 kg 275 g · Identify the original whole and the amount being removed · Understand a kilogram as a thousand grams · Represent the subtraction with a mass bar · Solve 2,150 − 875 using place value · Use a number line as an independent check · Verify the units, estimate and inverse relationship · Common errors tell the tutor what to repair first · Choose an attentive weekday tutoring window · Use a weekend session when a concrete model will help · How three-pupil instruction and four checkpoints support progress · Independent review: subtract 785 g from 3 kg 40 g · Parent questions · Consultation and class fit
The answer is 1 kg 275 g
A fictional package begins with 2 kg 150 g, and 875 grams are removed. The amount remaining is 1 kg 275 g.
Convert the starting mass into grams: two kilograms are 2,000 g, so 2 kg 150 g is 2,150 g.
Subtract the removed mass: 2,150 − 875 = 1,275 g. There is one complete group of a thousand grams in the remainder.
Convert that complete thousand to one kilogram, leaving 275 g. The result in the requested compound units is 1 kg 275 g.
Verify through addition: 1,275 + 875 = 2,150 g. The remainder and the removed contents exactly reconstruct the original mass.
The answer is smaller than the starting amount, as the story requires. A result such as 2 kg 725 g should immediately be questioned because it exceeds the starting mass.
The useful tutoring question is whether the pupil knows why the kilograms must be converted or exchanged, not only whether the final answer matches a model solution.
Identify the original whole and the amount being removed
Write the given measurements on separate cards: “starting mass 2 kg 150 g” and “mass removed 875 g”. Ask the child what is known and what remains unknown.
The starting mass is one quantity written in two different units. The 2 kg and 150 g are not two separate packages being compared.
The 875 g is the portion taken away. It should not be added to the initial mass or used as the total remaining.
Ask whether removing less than a kilogram from a package of a little over two kilograms should leave more than one kilogram. The answer is yes, which helps estimate before calculating.
A learner might try 875 − 150 because those are both displayed in grams. The story instead removes 875 from the entire 2 kg 150 g starting amount.
A bar diagram can make the meaning visible: the complete bar is the starting mass, with one part removed and another part unknown.
Preserve the child’s first independent equation. If it uses the wrong operation, begin with story interpretation; if the equation is correct but the units are confused, begin with conversion.
Understand a kilogram as a thousand grams
A kilometre is not involved in this question: the unit kg means kilogram, a unit of mass. A gram is smaller; 1 kg = 1,000 g.
Ask the pupil to turn two kilograms into grams. Two groups of a thousand give 2,000 g, and adding another 150 g gives 2,150 g.
The number 2,150 is an amount measured entirely in grams. It is not 2,150 kilograms and not an arbitrary concatenation of the digits two and one hundred fifty.
Use a marked mass bar showing one kilogram, another kilogram and an extra 150 grams. The total is the same mass whether labelled in compound units or in grams only.
Now show 1,275 g. One thousand of those grams can be exchanged for one kilogram, leaving 275 grams. Its conventional compound form is 1 kg 275 g.
If a learner writes 1 kg 1,275 g, the thousand grams are being counted twice. The conversion should remove the complete thousand from the gram remainder when it is expressed as a kilogram.
If the learner does not yet understand the exchange, practise simple equivalences before adding a subtraction algorithm. Reliable units are the foundation of this problem.
Represent the subtraction with a mass bar
Draw a long rectangle with two large portions labelled 1 kg each and a smaller portion labelled 150 g. It represents 2 kg 150 g in total.
Below it draw the portion that will be removed and label that portion 875 g. The mass removed is greater than the isolated 150 g section but smaller than a full kilogram.
To supply enough grams to remove 875 g, exchange one of the full kilograms into 1,000 g. Keep the other full kilogram untouched.
The new representation is 1 kg + 1,150 g. Its value remains 2 kg 150 g because no mass was created during the exchange.
Now remove 875 g from the 1,150 g section. That section retains 1,150 − 875 = 275 g.
The untouched kilogram and the remaining 275 g give the required result: 1 kg 275 g.
If the child adds the 1,000 g exchange to both original kilograms, the bar would show too much mass. The original kilogram being converted must no longer remain as a separate full kilogram.
A tutor can point to the bar while the child describes each action: which unit was exchanged, how much was removed, and what stayed in the parcel.
Solve 2,150 − 875 using place value
Work in grams, so the written expression is 2,150 − 875. Align the hundreds, tens and ones columns carefully.
In the ones column, zero cannot supply five ones. Exchange one ten into ten ones, leaving four tens. Ten minus five gives five ones.
In the tens column, four tens cannot supply seven tens. Exchange one hundred into ten tens, giving fourteen tens. Fourteen minus seven leaves seven tens.
In the hundreds column, the original one hundred has been exchanged. Exchange one of the two thousands into ten hundreds so the eight hundreds can be subtracted.
Ten hundreds minus eight hundreds leave two hundreds. One thousand remains, yielding 1,275 g.
The digits describe one thousand, two hundreds, seven tens and five ones, not four unrelated marks on a page.
Now record the compound measurement as one kilogram and 275 grams. That conversion step is needed because the question requests a value in kilograms and grams.
The tutor should make the carrying or exchanging explicit at least once; otherwise a copied column algorithm can look correct without a secure concept behind it.
Use a number line as an independent check
Begin at the smaller quantity of 875 g on a number line and count forward to the original amount of 2,150 g.
From 875 to 1,000 is 125 g. From 1,000 to 2,000 is exactly one thousand grams.
From 2,000 to 2,150 is another 150 g. The complete distance is 125 + 1,000 + 150 = 1,275 g.
This agrees with the written subtraction, even though the approach uses forward jumps rather than exchanging digits in the standard column layout.
A shorter two-jump route also works: 875 to 1,000 is 125, and 1,000 to 2,150 is 1,150. Together the jumps total 1,275.
A child who can reason with either number line is learning that subtraction measures the difference between two quantities, regardless of which method is used.
Count-up is not the same as adding the removed mass to the original. The line measures how far one quantity lies below the other.
Verify the units, estimate and inverse relationship
The reverse equation is 1,275 g + 875 g = 2,150 g. Check the addition carefully, including the necessary carries in tens and hundreds.
Express the addition in compound units as 1 kg 275 g plus 875 g. The gram parts total 1,150 g, which is one kilogram and 150 g.
Adding that new kilogram to the original one gives 2 kg 150 g, matching the starting mass.
For an estimate, 875 g is close to 900 g. Two thousand one hundred fifty minus about nine hundred should leave about one thousand two hundred fifty grams.
The exact 1,275 g is sensible. It is not plausible for a package to weigh more after mass has been removed.
If the pupil has the right digits but writes 1,275 kg, the numerical subtraction and the final measurement unit have diverged.
A complete explanation should always say which unit a number is using at that stage and why the final answer takes a different but equivalent form.
Common errors tell the tutor what to repair first
An answer of 2 kg 725 g may come from reversing 875 and 150 while leaving the original two kilograms intact. It overlooks the kilogram that must be exchanged.
An answer of 1 kg 1,275 g double-counts a kilogram. Ask how many grams remain after the complete thousand has been converted back to one kilogram.
A result of 1 kg 375 g may be an arithmetic error. Add it to 875 g and observe that the total is not the original 2,150 g.
A pupil who gets 1,275 g correctly but cannot write 1 kg 275 g needs the conversion step taught, not a complete repetition of subtraction.
Another student may use addition from the outset because both quantities appear in the story. Ask what the words “taken out” do to the original mass.
An explanation that relies solely on saying “borrow here” does not show whether the learner understands kilograms, hundreds or tens. A physical or bar model can reveal the missing quantity relationship.
The first unstable step should guide the tutoring, rather than assigning the same extra workbook exercise to every learner.
Choose an attentive weekday tutoring window
A weekday Primary 3 session can connect to a current school worksheet on compound mass. The pupil can bring the first uncorrected attempt and show where they stopped.
For Chiltern Park families, the nearby Lorong Chuan area helps with orientation, but the actual tuition venue must be confirmed before travelling or comparing lesson schedules.
A tired child can misalign the subtraction or overlook the final unit conversion despite having some understanding. Check food, travel, CCA and bedtime before booking.
A focused lesson might use a mass bar, a gram-only calculation, an inverse check and one new short question rather than many rushed repetitions.
Ask the tutor whether the child can now explain the exchange without being told where to move a small carried digit.
A delayed independent task on another day is more informative than repeating 2 kg 150 g minus 875 g at the end of the same class.
The selected slot should support attention and recovery, not simply fill a spare hour between other commitments.
| Factor | Weekday tuition | Weekend tuition |
|---|---|---|
| Recent schoolwork | Use an actual unit-conversion error promptly | May allow an unhurried kilogram model |
| Child’s attention | Check school finish, meals, travel and homework | Check sport, family activities and other lessons |
| Delayed review | New mass question on a separate day | Unfamiliar compound measurement during school week |
Use a weekend session when a concrete model will help
A weekend tutorial can provide a calmer start with kilogram and gram strips, useful when the student has memorised the conversion rule but cannot imagine how the units fit together.
The tutor can ask the pupil to build the original mass, exchange a kilogram into one thousand grams and predict the resulting parts.
The entire amount should remain unchanged during the exchange, which can be checked against the label 2,150 g.
Weekend sport, family events and enrichment can still make the day tiring. A longer session is not automatically more effective.
After using the model, the learner should perform the calculation in grams without needing someone else to assemble the bar again.
A new mass question during the following school week checks that the method transfers beyond the activity.
The goal is a child who can reason accurately, not simply an elaborate physical demonstration completed with the tutor.
How three-pupil instruction and four checkpoints support progress
One pupil may convert the starting mass correctly but subtract inaccurately. A second may calculate 1,275 g but write the wrong unit. A third may not understand the kilogram conversion.
The first needs arithmetic support; the second needs compound-unit recording; the third needs the equivalence of one kilogram and one thousand grams.
A true 3-pax tutorial should collect individual first attempts before one confident learner gives the answer to the whole group.
Week one can focus on reading compound masses. Week two can model kilogram exchanges. Week three can compare a gram-only subtraction with a counting-up check.
In week four, the tutor can present a fresh example after a delay and record whether the pupil converts, calculates and checks without hints.
These checkpoints are flexible, not a promised four-week timetable for every pupil. The child’s actual schoolwork and level of independence should guide the next task.
For further background, see the eduKate Primary 3 Mathematics study guide and Mathematics learning hub.
Independent review: subtract 785 g from 3 kg 40 g
Several days after tuition, give the pupil a different problem: a package has mass 3 kg 40 g, and 785 g is removed. Ask for the remaining mass in kilograms and grams.
The initial measurement is 3,040 g. Subtract 785 g to obtain 2,255 g.
Convert the result into compound units: two complete kilograms and 255 grams remain, so the answer is 2 kg 255 g.
Check through addition: 2,255 + 785 = 3,040 g. This reconstructs the original mass exactly.
For a shorter second question, calculate 1 kg 300 g − 650 g. Converting 1 kg 300 g to 1,300 g gives the remainder 650 g.
Ask why the second result contains no whole kilogram while the first result contains two. The values, not the word problem’s surface wording, determine the final compound units.
Preserve both independent attempts and the first hint given. Correct answers with sensible units and addition checks show stronger transfer than remembering the original 1 kg 275 g result.
Questions Chiltern Park parents ask
What is 2 kg 150 g minus 875 g?
It is 1,275 g, or 1 kg 275 g. Convert the starting mass into grams, subtract, and check by adding 875 g back.
What makes one kilogram?
One kilogram is one thousand grams, so the same mass can be represented using kilograms, grams, or a compound form.
Why is 1 kg 1,275 g not a suitable final answer?
It double-counts a thousand grams if the 1,275 g already represents the complete remainder. The conventional result is 1 kg 275 g.
Is this appropriate for Primary 3 Mathematics?
Yes. The updated Primary 3 syllabus includes compound measurements and conversions between kilograms and grams.
Should the lesson be on a weekday or weekend?
Either can work when the child is alert, the route is practical, and a tutor can check a new independent problem after the teaching.
Confirm an appropriate lesson and the real teaching venue
The MOE Primary Mathematics syllabus, updated October 2025, establishes the year-level content. The eduKate Primary 3 Mathematics guide and Mathematics learning hub connect this example to other measurement topics. It is a focused diagnostic, not a full syllabus test or a grade guarantee.
Chiltern Park is a residential area near Lorong Chuan on Serangoon Avenue 3. The Chiltern Park geographical reference and Lorong Chuan family-learning guide help families orient themselves, but do not establish that eduKate operates a tuition branch inside the development. Confirm the actual class venue, available 3-pax group, fees and journey directly.
For an eduKate parent–student consultation, bring a genuine first attempt, the earliest helpful prompt, the learner’s school level and the timetable that preserves rest and homework. Ask what a different compound-mass problem will look like when solved without coaching.
Compare the Lorong Chuan Primary 3 Mathematics tuition guide for another worked example at the same level.
Explore other Chiltern Park Primary Mathematics guides
Each guide below uses a different Mathematics skill, a fully worked example and an independent check to help parents compare suitable weekday and weekend learning routines.
- Primary 1: Subtraction across a ten
- Primary 2: Regrouping through zeroes
- Primary 4: Common factors of 36 and 48
For another neighbourhood-focused example at the same level, see Primary 3 Mathematics Tuition | Serangoon Avenue 3. Continue through the eduKate Mathematics learning hub for related topics.