Question

The traphic light at three different road crossing change after every 48 sec , 72 sec, 108 sec respectively. If they all change simultaneously at 8:20:00 hours., then at what time they again change simultaneously

Answer 1

the traffic light changes after 48,72,108 sec.
the time they change simultaneously again=LCM of 48, 72 ,108
48=2x2x2x2x3
72=2x2x2x3x3
108=2x2x3x3x3
LCM=2x2x2x2x3x3x3=432
thus they will after at 432 seconds
which is equal to 7 minutes and 12 seconds
then the time they will meet=8:20:00+00:07:12=8:27:12