UPSC 2014 CDS I Math Paper

In 60 minutes, hour hand will move 5-minute spaces while the minute hand will move 60-minute spaces.
Gain of 55-minute spaces = 60minutes
Gain of 15-minute spaces
=

60

55

×15=16

4

11

minutes. This is the number of minutes after which minute hand and hour hand coincide. Now, after further 16

4

11

minutes, the minute and hour hand would be at right angle.
Therefore, time after 3 o’clock, the hour hand and minute hand are at right angle.
=3‌hours+16

4

11

‌min+16

4

11

‌min
=3‌hours‌32‌

8

11

‌minutes