A man in a train notices that he can count 21 telephone posts in one minute. If they are known to be 50 metres apart, at what speed is the train travelling?
61 km/hr
56 km/hr
63 km/hr
60 km/hr
Explanation:
The man in the train notices that he can count 21 telephone posts in one minute.
Number of gaps between 21 posts are 20 and Two posts are 50 metres apart.
It means 20 x 50 meters are covered in 1 minute.
Distance = $20 \times 50$meter = $\dfrac{20 \times 50}{1000}$km = 1 km
Time = 1 minute = $\dfrac{1}{60}$hour
Speed = $\dfrac{Distance}{Time} = \dfrac{1}{(\dfrac{1}{60})}$ = 60km/hr