CSS General Science 2019 Q.6(a) Solved

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CSS Paper: General Science 2019 Q.6(a)
Moiz was trying to sleep at one night but there was too much noise around him. His clock ticked every 5 second: a tap was dipping every 7 second and a pet dog snored every 12 second. He noticed on his clock that all three things happened together on the stroke of mid night. Find after how many seconds all three things happened together again?

This is an application of LCM (Least Common Multiple). So,

And, 2×2×3×5×7 = 420
Hence, after 420 seconds all three things will happen together again. Answer.