How many times are an hour hand and a minute hand of a clock at right angles during their motion from 1.00 p.m. to 10.00 p.m.?  

(a) 9 (b) 10 (c) 18 (d) 20

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1 Answers

(c) In one hour, hour hand and minute hand are at right angles 2 times.

Time = 10 p.m – 1 p.m = 9 hr.

∴ No. of times, when both hands are perpendicular to each other in 9 hr = 9 × 2 = 18

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