4 high-yield, syllabus-aligned questions on Financial mathematics, covering 11 individually creditable mark points. Each one shows the answer that scores full marks under our guide, which phrase earns which mark, and a common incomplete answer — so you can see the difference rather than guess at it.
Free to read. No account needed for anything on this page.
Every question and solution is reviewed by examiners versed in WAEC and JAMB, each with more than thirty years of experience.
Mark allocations are TopMarks’ own, written against the published syllabus and Chief Examiners’ reports. They are a guide to how these answers are usually credited, not an official marking scheme.
Calculate3 marks
A trader bought an article for ₦24,000 and sold it for ₦30,000. Calculate the percentage profit.
2Percentage profit = (profit ÷ COST price) x 100 — The denominator is the cost price, always. Using the selling price is the single commonest error in the topic.
3= (6000 ÷ 24000) x 100 = 25% — State the answer as a percentage.
Why it scores
Percentage profit is always calculated on what you PAID, not on what you received. Dividing by the selling price here gives 20% — a plausible-looking answer that is simply wrong, and one the mark scheme specifically watches for.
A common incomplete answer
“Profit = ₦6,000, so the percentage profit is (6000 ÷ 30000) x 100 = 20%.”
What it costs: Two marks of three. The profit is right, but the percentage has been taken on the selling price instead of the cost price, so both the method and the answer are wrong.
Calculate the simple interest on ₦45,000 for 3 years at 8% per annum.
TopMarks model answer
Simple interest I = (P x R x T) ÷ 100, where P is the principal, R the rate per annum and T the time in years. I = (45000 x 8 x 3) ÷ 100 = 1080000 ÷ 100 = ₦10,800.
Suggested marking guide
1Correct formula stated
2Correct substitution
3Correct answer
The working, line by line
1I = (P x R x T) ÷ 100 — Write the formula. It is a mark whether or not the arithmetic that follows is right.
2I = (45000 x 8 x 3) ÷ 100 — P = 45000, R = 8, T = 3. The rate goes in as 8, not 0.08, because the formula already divides by 100.
3I = ₦10,800 — This is the INTEREST. If the question had asked for the amount, you would add the principal: ₦55,800.
Why it scores
Read the last line of the question carefully. “Interest” and “amount” are different quantities: the amount is the interest PLUS the principal. Answering the wrong one gives away every mark on an otherwise perfect calculation.
A common incomplete answer
“I = 45000 x 8 x 3 = 1080000”
What it costs: Two marks of three. The substitution is credited, but the division by 100 is missing, so the answer is a hundred times too large and the formula was never stated.
Key ideas to include: principal, rate per annum, time in years, simple interest, amount.
Calculate3 marks
The value of a machine depreciates by 10% each year. If the machine cost ₦500,000 when new, calculate its value after 2 years.
TopMarks model answer
After a depreciation of 10%, the machine retains 90% of its value each year. Value after 1 year = 90% of 500000 = 0.9 x 500000 = ₦450,000. Value after 2 years = 0.9 x 450000 = ₦405,000.
Suggested marking guide
1Recognises that 90% is retained each year
2Correct value after one year
3Correct value after two years
The working, line by line
1Depreciating by 10% means keeping 90%, so multiply by 0.9 each year — Working with what REMAINS is far quicker and safer than subtracting the loss each time.
2After 1 year: 0.9 x 500000 = ₦450,000 — Show each year separately. Each is a mark.
3After 2 years: 0.9 x 450000 = ₦405,000 — The second year’s 10% is taken on the REDUCED value, not on the original.
Why it scores
Depreciation compounds. The second year’s 10% is taken on ₦450,000, not on the original ₦500,000, so the total loss is ₦95,000 rather than ₦100,000. Treating each year as 10% of the original is the mistake this question exists to catch.
A common incomplete answer
“Depreciation = 20% of 500000 = 100000, so the value is ₦400,000.”
What it costs: All three marks. The two years’ depreciation cannot be added as 20% of the original, because the second year is calculated on the already-reduced value.
Key ideas to include: depreciation, percentage decrease, compounding, reduced value.
Explain2 marks
Explain the difference between simple interest and compound interest.
TopMarks model answer
Simple interest is calculated on the original principal only, so the interest earned is the same in every period. Compound interest is calculated on the principal together with the interest already earned, because the interest is added to the principal at the end of each period, so the amount grows faster and by an increasing amount each year.
Suggested marking guide
1Simple interest is on the original principal only
2Compound interest includes the interest already earned
Why it scores
Each mark belongs to one side of the comparison, so both must be given. The phrase that earns the second mark is the idea of interest being ADDED TO THE PRINCIPAL — that is what makes compound interest compound, and it is what makes the yearly interest grow.
A common incomplete answer
“Compound interest gives you more money than simple interest.”
What it costs: Both marks. It states an outcome rather than a difference in method, and neither the original principal nor the adding of interest to the principal is mentioned.
Key ideas to include: principal, simple interest, compound interest, amount, per annum.
Practise Financial mathematics on real questions
Reading a full-mark answer is the first half. Writing one under time is the other. A free account opens exam-standard practice in Mathematics with the full solution on every question.