Question

There are three athletes A, B and C at a same point. A starts running from a point at a speed of 50 m/min. After 5 minutes, B starts running towards A with a speed of 60 m/min. Determine at what speed C should start running to cross A and B together, if C starts running 5 minutes after B.

1. 65 m/min
2. 70 m/min
3. 75 m/min
4. 80 m/min

Answer 1

Correct Answer - Option 3 : 75 m/min

Let’s assume A, B and C cross each other t min after A starts running.

Let V be the required speed(m/min) of C to cross A and B together.

When A, B and C cross each other ⇒ 50 × t = 60 × (t – 5) = V × (t – 10)

⇒ 50 × t = 60 × (t – 5)

⇒ 5t = 6t – 30

⇒ t = 30 min

Now, V = 50 × t/(t – 10) = 50 × 30/(30 – 10) = 1500/20 = 75 m/min