SOLUTION: the traffic light at three different road crossings change after every 48,72 and 108 sec,.if they all change simultaneously at 8:20:00 hrs, then at what time will they again change

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Question 895830: the traffic light at three different road crossings change after every 48,72 and 108 sec,.if they all change simultaneously at 8:20:00 hrs, then at what time will they again change simultaneously?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Find the LCM of 48, 72, and 108.
48=2%2A2%2A2%2A2%2A3=2%5E4%2A3
72=2%2A2%2A2%2A3%5E2=2%5E3%2A3%5E2
108=2%2A2%2A3%2A3%2A3=2%5E2%2A3%5E3
So then,
LCM=2%5E4%2A3%5E3=16%2A27=432
So count 432 seconds from 8:20.
432 seconds equals 7 minutes 12 seconds.
8:20:00 + 0:07:12=8:27:12