A wall clock moves 10 minutes fast in every 24 hours. The clock was set right to show the correct time at 8:00 a.m. on Monday. When the clock shows the time 6:00 p.m. on Wednesday, what is the correct time?
Answer & explanation
Answer: (a) 5:36 p.m.
The clock shows 24 h 10 min for every 24 real hours. It shows 58 hours gone, which is 58 × 1440/1450 = 57.6 real hours (57 h 36 min), so the correct time is 5:36 p.m. on Wednesday.
- From 8:00 a.m. Monday to 6:00 p.m. Wednesday the clock shows 48 + 10 = 58 hours.
- Shown time : real time = 24 h 10 min : 24 h = 1450 : 1440.
- Real time = 58 × 1440/1450 = 57.6 h = 57 h 36 min.
- Correct time = Monday 8:00 a.m. + 57 h 36 min = Wednesday 5:36 p.m.
- Check: gain = 10 min × 57.6/24 = 24 min, and 6:00 − 0:24 = 5:36.
Remember · For a fast or slow clock, convert shown time to real time by the ratio real : shown, not by a flat subtraction.
Question and answer: UPSC's official GS Paper II (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·