Question

traffic light at 3 road crossing change after every 48 seconds,72 seconds,108 seconds.they change simultaniously at 8 am.what time will they change again?

Answer 1

The common multiple between the three numbers is 3456. 
48 * 72 = 3456 
72 * 48 = 3456 
108 * 32 = 3456 
So, the next time the lights change simultaneously is 3456 seconds later or 57 minutes 36 seconds later. If it's 7am now, it will change at 7:57 and 36 seconds

Answer 2

Traffic lights change for every 48, 72, 108 seconds

LCM of 48, 72, 108 is 432

That means, after 432 seconds, all the three lights will changes

That means, after 7 min 12 seconds.

therefore, they will change at 08:07:12 am.