​A man travelling in a train notices that he can count 21 telephone posts in 1 min. If the poles are 50 m apart, then at what speed is the train travelling? ​

Correct option is C

Given:

Number of telephone posts: 21

Distance between poles: 50 m

Time taken to count 21 poles: 1 minute

Formula Used:

Speed = $$\frac{\text{Distance }}{\text{ Time}}$$​​

Solution:

Calculate Total Distance Covered:

Distance between 21 poles = (Number of poles - 1) $$\times$$ Distance between each pole

Distance = (21 - 1) $$\times$$50 m = 20$$\times$$ 50 m = 1000 m

Convert Time to Seconds:

Time = 1 minute = 60 seconds

Calculate Speed:

Speed = $$\frac{1000 m }{60 s}$$​​

Speed = 16.67 m/s

To convert to km/h:

= $$\frac{1000 m }{60 s} \times \frac{18}{5}$$​​

= 60 km/h

Therefore, the speed of the train is 60 km/h.

Option (C) is right answer