Question

On a Road, three consecutive traffic lights change after 36, 42 and 72 seconds respectively. If the lights are first switched on at 9 a.m sharp, at what
time will they change simultaneously

Answer 1

They will change simultaneously after a time which is a common multiple of 36, 42 and 72 seconds = LCM (36, 42 and 72 seconds) = 504 Seconds = 8 mins and 24 seconds

So the next time = 9:08:24