Clocks

Geometry Level 3

Find the angle (in minutes) between the minute and the hour hand of a clock at 9:38 in minutes.

Clarification: One degree is equivalent to 60 minutes.


The answer is 3660.

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1 solution

Chew-Seong Cheong
Jan 13, 2017

At 9:00 the hour-hand is at 270 ^\circ . Since the hour-hand moves 360 ^\circ in 12 hours, therefore it moves 36 0 12 × 60 = 1 2 \dfrac {360^\circ}{12\times 60} = \dfrac 12^\circ /min. Therefore by 9:38 minutes, it advances by 38 × 1 2 = 1 9 38 \times \dfrac 12 = 19^\circ to 270 + 19 = 28 9 270+19=289^\circ . At 9:38 the minute-hand is at 38 60 × 36 0 = 22 8 \dfrac {38}{60} \times 360^\circ = 228^\circ . The angle between the minute- and hour-hand at 9:38 is 28 9 22 8 = 6 1 = 61 × 60 = 3660 289^\circ-228^\circ = 61^\circ = 61 \times 60 = \boxed{3660} minutes.

It must be 10.167 minutes.

By ratio and proportion, we have

x ( m i n s ) 61 ° = 30 m i n s 180 ° \frac{x (mins)}{61°}=\frac{30 mins}{180°}

x = 10.167 x=10.167 m i n u t e s minutes

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