A town has males and females in a ratio of 3:2. After 5 years, the male population increases by 10%, and the female population by 25%. What is the new ratio?

Correct — B. Take the ratio as actual numbers: males 3, females 2. Any common multiple gives the same answer.

Males rise 10%: 3 × 1.10 = 3.3
Females rise 25%: 2 × 1.25 = 2.5

New ratio = 3.3 : 2.5
Multiply both terms by 10: 33 : 25 (no common factor) → option (b)

Why the others are wrong

• (a)
  3:2.5 — 3 : 2.5 raises the females by 25% but leaves the males at 3, dropping the 10% rise in males. It is the same ratio as 6 : 5.
• (c)
  66:65 — 66 : 65 = 3.3 : 3.25. The male side is right, but 3.25 would mean the females grew from 2 by 62.5%, not 25%. Correctly, 2 × 1.25 = 2.5.
• (d)
  6:5 — 6 : 5 is 3 : 2.5 in whole numbers, so again only the female rise is applied. With both rises, 3.3 : 2.5 = 33 : 25, not 30 : 25.

When each part of a ratio grows by its own percentage, scale each part by its own multiplier, then simplify.

A 10% rise is × 1.10 and a 25% rise is × 1.25. The ratio shifts towards the females because their number grows faster.

New ratio = (3 × 1.10) : (2 × 1.25) = 3.3 : 2.5. The actual population is never needed.

Key facts

• An x% rise multiplies a quantity by (1 + x⁄100): 10% gives × 1.10 and 25% gives × 1.25
• Multiplying both terms by the same number keeps a ratio unchanged: 3.3 : 2.5 = 33 : 25
• Equal percentage rises leave a ratio unchanged, while unequal rises change it

Common traps

• Applying only one of the two rises, which gives 3 : 2.5 = 6 : 5
• Compounding the rises over the 5 years when the stem gives one total change per group

No directly related past PYQ was found.