Q. 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.?
Answer:
18
Notes: 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.