The traffic lights at three different road crossings change after 24 seconds, 36 seconds and 54 seconds respectively. If they all change simultaneously at 10 : 15 :00 AM, then at what time will they again change simultaneously?
The LCM of 24 seconds , 36 seconds and 54 seconds will give the next instance when all the three lights will change simultaneously.
LCM of 24 , 36 and 54 is 216.
216 seconds is equal to 3 minutes and 36 seconds.
The next instance when all the three lights will change simultaneously is 3 minutes and 36 seconds after 10 : 15 :00 AM which is at 10 : 18 : 36 AM.
Hence Option B is the correct answer.
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