Two numbers X and Y are respectively 20% and 28% less than a third number Z. By what percentage is the number Y less than the number X?
Answer & explanation
Answer: (b) 10%
Take Z = 100: then X = 80 and Y = 72. Y is 8 less than X, and measured against X that is 8/80 = 10%.
- Let Z = 100. Then X = 80 and Y = 72.
- Y is less than X by 80 − 72 = 8.
- As a percentage of X: 8/80 × 100 = 10%.
Remember · 'By what % is Y less than X' uses X as the base. Taking the reference number as 100 avoids fractions.
Question and answer: UPSC's official GS Paper II (2016, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·