Quantitative Reasoning – Practice – Accurate clock: a good one!


PSA_PRACTICE_QNR31. An accurate clock shows exactly 3 pm. In how many minutes will the minute hand catch up with the hour hand?

Ans: Questions on clock are similar in nature with time,speed and distance questions. The distance is usually in degrees. The second, minute and hour hands have constant speeds.

Minute hand covers 360 deg. in 1 hr or 60 minutes. Speed = 360/60 = 6 deg/min

Hour hand covers 360 deg. in 12 hrs or 12*60 minutes. Speed = 360/12*60 = 1/2 deg/min

Initially the clock shows 3 pm: the minute and hour hands are separated by 90 deg.

Relative speed of minute hand (w.r.t hour hand)= 6-1/2= 11/2 deg/min

Time needed to cover 90 deg= 90/(11/2) = 180/11 min.

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