Question

(4) We observed the traffic lights at three different squares on the same big road. They
turn green every 60 seconds, 120 seconds and 24 seconds. When the signals were
switched on at 8 o'clock in the morning, all the lights were green. How long after
that will all three signals turn green simultaneously again?
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Answer 1

So, all three signals turn green simultaneously again after a time interval which is the LCM of 60 seconds, 120 seconds, and 24 seconds. Multiples of 24: 24, 48, 72, 96, 120, 144, 168,... Common multiples of 60, 120, and 24: 120, 240,... Thus, all three signals turn green simultaneously again after 120 seconds.