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

Correct Answer : B.

       Interval of change = (L.C.M of 48,72,108)sec.=432sec.

       So, the lights will again change simultaneously after every 432 seconds =7 min.12sec

       Hence , next simultaneous change will take place at 8:27:12 hrs.