Question

The traffic lights at three different road junctions change after every 40 seconds, 60 seconds and 72 seconds respectively. If they changed simultaneously together at 8 a.m at the junctions, at what time will they simultaneously change together again?

Answer 1

This is an LCM related problem

Finding the LCM of 40, 60 and 72

60 seconds = 1 min

360 min = 6 min

2	40, 60, 72
2	20, 30, 36
3	10, 15, 18
5	10, 5, 6
2	2, 1, 6
3	1, 1, 3
	1, 1, 1

LCM (40, 60, 72) = 2 × 2 × 3 × 5 × 2 × 3 = 360

After 360 seconds they will change again i.e after six minutes they will change again i.e at 8.06 am they will change again simultaneously.