Question

How many times are the hands at right angles from 1 a.m. to 10 p.m.?

• A. 39
• B. 38
• C. 32
• D. 40

Answer 1

The correct option is B 38

Every 12 hours, the hands are right angles 22 times. So For every 180 degrees that the minute hand gains on the hour hand there will be one 90 degree angle, so every 49 1/11 - 16 4/11 = 32 8/11 minutes. So, in 21 hours = (1260*11)/(360)