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

8 : 27 : 12 hrs.
8 : 27 : 24 hrs.
8 : 27 : 36 hrs.
8 : 27 : 48 hrs.

Correct Answer: 8 : 27 : 12 hrs.

Explanation:

Interval of changes = (L . C . M of 48, 72, 108) sec. = 432 sec.
So, the lights will simultaneously changes after every 432 seconds i,e 7 min. 12 sec.
So, the next simultaneously changes will take place at 8 : 27 : 12 hrs.

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