Question

In a circular race of 1500 metres, M and N start running simultaneously with speeds of 27 km/h and 45 km/h from the same point and at the same time. After how much time will they meet at the starting point for the first time if they are running in the same direction?

• A. 5 min
• B. 10 min
• C. 12 min
• D. 15 min

Answer 1

The correct option is B 10 min

Speeds of M and N are 27 × (5/18) = 7.5 m/s and 21.5 m/s, respectively.

Time taken by M to complete one round = 1500/7.5 = 200 sec

Time taken by N to complete one round = 1500/12.5 = 120 sec

Time after which they will again meet for the first time at the starting point will be the LCM of the time taken by them to complete one round.

i.e., LCM (200, 120) = 600 seconds or 10 minutes

Hence, option (B) is the correct answer.