Secondary 3 G2 Mathematics Tutor Bukit Timah | Compound Interest and Depreciation Models. Did you know? A percentage applied repeatedly changes its own starting amount.
This Secondary 3 G2 Mathematics guide for Bukit Timah learners explains compound interest and depreciation models using worked examples, interpretation checks and independent practice. Follow the student’s current school chapter sequence.
Compound growth
For an illustrative initial $1000 at 5% annual compound growth, after three years the amount is 1000(1.05)^3=$1157.625, or $1157.63 to the nearest cent.
Explain the relationship in words before using a formula. Then change one number and check whether the same method still works. The aim is independent reasoning rather than memorising one example.
Simple versus compound
Simple interest on $1000 at 5% for three years adds $150, giving $1150. Compound growth gives about $1157.63 because each year’s increase is included in the next year’s base.
Explain the relationship in words before using a formula. Then change one number and check whether the same method still works. The aim is independent reasoning rather than memorising one example.
Depreciation
An illustrative asset worth $2000 falling 10% annually is worth 2000(0.9)^2=$1620 after two years under a fixed percentage model.
Explain the relationship in words before using a formula. Then change one number and check whether the same method still works. The aim is independent reasoning rather than memorising one example.
Reverse a change
If an amount becomes $121 after two 10% increases, its initial value was 121/(1.1)^2=$100.
Explain the relationship in words before using a formula. Then change one number and check whether the same method still works. The aim is independent reasoning rather than memorising one example.
Why percentages do not add
Two consecutive 10% increases produce multiplier 1.1×1.1=1.21, a total 21% rise, not 20%.
Explain the relationship in words before using a formula. Then change one number and check whether the same method still works. The aim is independent reasoning rather than memorising one example.
Real-world limitation
These are simplified mathematical examples, not quoted bank rates or financial advice. Fees, taxes and changing rates require additional terms.
Explain the relationship in words before using a formula. Then change one number and check whether the same method still works. The aim is independent reasoning rather than memorising one example.
Check
The amount should rise under positive compound growth and fall under positive depreciation. Identify the starting amount and number of periods before calculating.
Explain the relationship in words before using a formula. Then change one number and check whether the same method still works. The aim is independent reasoning rather than memorising one example.
A seven-day revision routine
Day 1: identify the key quantities and units. Day 2: practise the first worked example. Day 3: vary one condition. Day 4: solve a question without the topic label. Day 5: correct the first mistaken step. Day 6: combine this skill with another Mathematics topic. Day 7: retest independently after a delay.
Frequently asked questions
What should I do first? Identify what is known, what is required and which conditions stay fixed. How do I check an answer? Substitute it into the original information, check units and test whether its magnitude makes sense. Why can the final number be wrong despite correct arithmetic? The equation or model may represent the wrong quantity.
Official syllabus and local tutorial context
Check the 2027 SEC G2 Mathematics K210 syllabus for the relevant topic and examination conditions. The unchanged eduKateSG Mathematics tutorial reference describes three-pupil small-group learning near Sixth Avenue. Confirm current Secondary 3 G2 availability, teacher, fees and timetable directly.
Related Secondary 3 G2 Mathematics guides
Continue with Reverse Percentages and Original Prices, Frequency Tables and Estimated Mean or Linear Graph Intersections.