Question

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 hours $8:20:00$, then at what time will they again change simultaneously ?

• A. $8:20:08 hrs$
• B. $8:24:10 hrs$
• C. $8:27:12hrs$
• D. $8:30:15hrs$

Answer 1

Answer: (C)

$8:27:12hrs$

Answer 2

The correct option is (C): L.C.M of $(48,72,108)=432$
They will all change simultaneously after 432 seconds = 7 min 12 seconds
$\therefore$Time they will change again = $8:20:00 + 00:07:12 = 8:27:12$ hours