Question

The traffic lights at 3 different roads change after every 12 seconds, 24 seconds and 72 seconds respectively. If they simultaneously at 6 A.M, at what time will they change again simultaneously?

Answer 1

They will change again simultaneously when the three timings reach there least common multiple.

the least common multiple of 12, 24, and 72 is 72

so the time they change simultaneously is after one minute 12 seconds.

that is 6 : 01 : 12

Answer 2

Answer is in Attachment !