1997 General Studies, all questions
UPSC Prelims 1997 · General Studies
Question 150: Logical Reasoning and Mental Ability
The number of times in a day the Hour hand and the Minute hand of a clock at right angles is
a44
b48
c24
d12
AnswerThe answer is (a).
The minute hand gains 11/12 of a turn per hour on the hour hand, so in 12 hours the hands make 11 relative turns. In each relative turn the hands are at right angles twice, so this happens 22 times in 12 hours and 44 times in a day.
Why each option is right or wrong
- (a) Right: 2 × 11 × 2 = 44 times in a day.
- (b) 48 assumes two right angles in every hour, but the 12-hour total is 22, not 24.
- (c) 24 counts only one right angle per hour.
- (d) 12 counts only one right angle per hour of a half-day.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1997, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.