There are three traffic signals. Each signal changes colour from green to red and then from red to green. The first signal takes 25 seconds, the second signal takes 39 seconds and the third signal takes 60 seconds to change the colour from green to red. The durations for green and red colours are same. At 2:00 p.m, they together turn green. At what time will they change to green next, simultaneously ?

By admin March 10, 2025No Comments

(UPSC CSAT – 2023)

Solution: Ans.(2)

Time taken by three signals to change green to green again are:

1^st signal : 25 sec. × 2 = 50 sec.

2^nd signal : 39 sec. × 2 = 78 sec.

3^rd signal : 60 sec. × 2 = 120 sec.

LCM = 7800 sec. = 2 hours 10 min.

2:00 p.m. + 2 hours 10 minutes = 4:10 p.m.

All the signals will change again green at 4:10 p.m.

Last updated on March 10, 2025

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