Quantitative Aptitude Clocks Study Material
A Clock is a device which shows Time. It essentially consists of two hands — an hour hand and a minute hand. The minute hand is longer than the hour hand. For simplicity, we will not consider the third hand — the second hand which is also present in many clocks and watches. Conventionally clocks are circular in shape but we can now find them in other different shapes too. Irrespective of the shape of the dial of the clock, the tips of their hands — hour as well as minute—describe a circular path. The circumference of this circular path is divided into 12 equal parts, called Hour spaces. Each hour space is farther divided into 5 equal parts called Minute spaces. Thus the complete circumference is divided into 12 x 5 = 60 equal minute spaces.
We know that 1 hour equals 60 minutes. Therefore, the time taken by the hour-hand to move one hour-space (or 5 minute-spaces) equals the time taken by the minute-hand to move 60 minute-spaces (or 12 hour-spaces) which is equivalent to covering the complete circumference. In other words, while the hour-hand moves one hour-space, the minute-hand goes one full circle.
From the above description we notice that in 1 hour (or 60 minutes), the minute-hand passes 60 minute-spaces while the hour-hand moves 5 minute-spaces. Thus, we may conclude that in 1 hour or 60 minutes, the minute-hand gains (60 - 5) = 55 minute-spaces (or minutes) over the hour-hand. This is a very important and useful conclusion and therefore, must be always remembered while solving problems on clock.
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