2015 CSAT, all questions
UPSC Prelims 2015 · CSAT
Question 68: Logical Reasoning and Mental Ability
Between 6 PM and 7 PM the minute hand of a clock will be ahead of the hour hand by 3 minutes at
a6 : 15 PM
b6 : 18 PM
c6 : 36 PM
d6 : 48 PM
AnswerUPSC’s answer is (c).
At 6:00 the minute hand is 30 minute-spaces behind the hour hand (180 degrees). The minute hand gains 5.5 degrees per minute on the hour hand. To be 3 spaces ahead it must gain 33 spaces, which is 198 degrees. Time = 198 ÷ 5.5 = 36 minutes, so 6:36. Check at 6:36: the minute hand is at 216 degrees and the hour hand at 198 degrees, so the minute hand is 18 degrees, or 3 spaces, ahead.
Why each option is right or wrong
- (a) Wrong: at 6:15 the minute hand is still about 16 spaces behind the hour hand.
- (b) Wrong: at 6:18 the minute hand is still about 13 spaces behind.
- (c) Right: at 6:36 the minute hand is at 36 and the hour hand at 33, three spaces ahead.
- (d) Wrong: at 6:48 the minute hand is at 48 and the hour hand at 34, 14 spaces ahead.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2015, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.