# Puzzle 4) Rohan and Traffic light

Submitted by Amit Shukla, on August 05, 2017

Puzzle

In Delhi a boy named Rohan lives. Rohan have a tea stall in Delhi which is run by his father. One day his father told Rohan to sit in the shop for a day. There are three traffic lights in front of its tea stall. The first light changes after 30 seconds, second light changes after 45 second and third light changes after 60 seconds. Rohan observes that after some time all three lights changes simultaneously. If the lights first switched on at 12: 00 PM, then you have to tell after how much time the lights changes simultaneously?

Important points of puzzle:

1. There are three traffic light in front of Rohan’s tea stall.
2. First light changes after 30 seconds, second after 45 seconds and third after 60 seconds.
3. Rohan observes that after some time all the light changes simultaneously.
4. If lights switched on at 12: 00 PM.
5. After how much time all three lights changes simultaneously.

3 Minutes.

Reason

We can find the time interval by taking LCM of 30, 45 and 60. The LCM of 30, 45 and 60 is 180. Which means that all three lights changes simultaneously after 180 Seconds. Hence the answer is 3 Minutes.