Why do percentages and ratio matter in S2?

S2 applies percentages to discounts, profit, growth and interest, and ratio to sharing and map scales; the two often appear in one question and underpin school tests and the DSE.

Why find the value of one part first?

In ratio sharing, find the total number of parts, then the value of one part, then multiply by each share, so every step can be checked.

S2 Maths: Percentages and Ratio (Error Correction, 10 Questions)

2026-11-06

Tutor Prep Guide · S2 Mathematics

Ten error-correction items on the traps S2 students fall into: dividing instead of multiplying for a percentage of a quantity, treating the discount as the price, dividing the change by the new value, wrong multipliers in reverse questions, mixed units in a ratio, forgetting the total parts, linked ratios without a bridge term, scales without unit conversion, assuming equal up and down percentages cancel, and the wrong denominator in a percentage comparison. Each item has an answer and a note.

Quick answer Answers in order: 36, 280 dollars, 15%, 120, 3 : 4, 270 dollars, 8 : 15, 2 km, 96%, 25%. Write original x multiplier = new value before substituting, and unify units first.

01 Paper details (check answers afterwards)

Item	Detail
Questions	10 questions
Suggested time	about 30 minutes
Difficulty mix	Error redo 10
Chapter	Chapter: S2 Maths: Percentages and Ratio
Level	S2

02 Questions (10 items)

Error redoFind 15% of 240.
Error redoAn item costs 350 dollars and is sold at a 20% discount. Find the selling price.
Error redoA value rises from 80 to 92. Find the percentage increase.
Error redoA number becomes 150 after increasing by 25%. Find the number.
Error redoSimplify the ratio 45 minutes : 1 hour.
Error redoShare 720 dollars between A and B in the ratio 5 : 3. How much does B get?
Error redoA : B = 2 : 3 and B : C = 4 : 5. Find A : C.
Error redoA map has a scale of 1 : 25000. What real distance does 8 cm represent in km?
Error redoAn item is cut by 20% and then raised by 20%. What percentage of the original price is left?
Error redo60 is what percentage of 240?

03 Answers and one-line notes

#	Answer	One-line note
1	36	A percentage of a quantity means multiply: 240 x 0.15 = 36.
2	280 dollars	A 20% discount means paying 80%, so 350 x 0.8 = 280 dollars.
3	15%	Divide the change by the original value: 12 / 80 = 0.15, which is 15%.
4	120	Reverse the increase by dividing: 150 / 1.25 = 120.
5	3 : 4	Convert to the same unit first, then divide both terms by 15 to get 3 : 4.
6	270 dollars	There are 8 parts of 90 dollars each, so B gets 3 parts, which is 270 dollars.
7	8 : 15	Link through B: A/C = 2/3 x 4/5 = 8/15, so A : C = 8 : 15.
8	2 km	8 x 25000 = 200000 cm, which is 2000 m or 2 km; forgetting the unit change gives 200 km.
9	96%	0.8 x 1.2 = 0.96, so 96% of the original price remains.
10	25%	Divide by the number after “of”: 60 / 240 = 0.25, which is 25%.

04 What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

Find a tutor free Tutor Registration →

Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.