If 7 24 = 25 and 12 16 = 20, then what is 16 * 63 equal to?
Answer & explanation
Answer: (c) 65
Both examples are Pythagorean triples: 7, 24, 25 and 12, 16, 20. So a b means √(a² + b²), and 16 63 = √(256 + 3969) = √4225 = 65.
- 7² + 24² = 49 + 576 = 625 = 25², and 12² + 16² = 144 + 256 = 400 = 20². So a * b = √(a² + b²).
- 16 * 63 = √(16² + 63²) = √(256 + 3969) = √4225 = 65.
- Check: 65² = 4225.
Remember · When results look like hypotenuses, test √(a² + b²); know common triples such as 7-24-25 and 16-63-65.
Question and answer: UPSC's official GS Paper II (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·