A student's marks in Mathematics were 20% more than in Physics. If he scored 72 in Physics, how many marks did he score in Mathematics?

Correct — D.
The base is Physics: 72 marks
20% of 72 = 0.2 × 72 = 14.4
Add it on: 72 + 14.4 = 86.4 → option (d)

The same in one step: 72 × 1.2 = 86.4

Why the others are wrong

• (a)
  82.4 — 82.4 is only 10.4 above 72, which is about 14% more than Physics. The question says 20%, and 20% of 72 is 14.4.
• (b)
  88.4 — 88.4 is 16.4 above 72, about 22.8% more than Physics — it overshoots the 20% the question states.
• (c)
  84.4 — 84.4 is 12.4 above 72, about 17.2% more. The increase has to be 20% of 72, which is 14.4, not 12.4.

'x% more than B' puts B in the denominator: the increase is x% of B, so the new value is B × (1 + x⁄100).

Here B is the Physics mark, 72, so Mathematics = 72 × 1.2.

Turning a percentage into a multiplier saves a step: 20% more is × 1.2, 20% less is × 0.8, 25% more is × 1.25.

Key facts

• A is x% more than B means A = B × (1 + x⁄100)
• 20% more = × 1.2 and 20% less = × 0.8
• If A is 20% more than B, then B is 16⅔% less than A

Common traps

• Taking 20% of the Mathematics mark instead of the Physics mark — the base is the quantity after 'than'
• Assuming Physics is then 20% less than Mathematics, when it is 16⅔% less

No directly related past PYQ was found.