Question

P, Q and R start running around a circular field having circumference 100 metre at the same time from the same point. Speeds of P, Q and R are 5 m/s, 15 m/s and 25 m/s. Find after how much time, they will meet again at the same point for the first time. 

1. 60 seconds
2. 15 seconds
3. 20 seconds
4. 40 seconds

Answer 1

Correct Answer - Option 3 : 20 seconds

Time taken by P to complete one round = 100/5 = 20 s

Time taken by Q to complete one round = 100/15 = 20/3 s

Time taken by R to complete one round = 100/25 = 4 s

L.C.M. of the frequency of P, Q and R = L.C.M. of (20, 20/3, 4) = 20 s

Thus, P, Q and R will meet again at the same point for the first time after 20 seconds.