Question

A railway passenger counts the telegraph posts on the line as he passes them while travelling. If the poles are 50m apart and the train is going at the speed of 48$km/hr$. How many posts will be passed by the train per minute?
$
  {\text{A}}{\text{. 16}} \\
  {\text{B}}{\text{. 17}} \\
  {\text{C}}{\text{. 18}} \\
  {\text{D}}{\text{. 20}} \\
$

Answer 1

Hint – To find the number of posts per minute, we convert the speed of train into$\dfrac{{\text{m}}}{{{\text{min}}}}$. Then we find the distance travelled in 1minute which helps us find number of posts in this distance.

Complete Step-by-Step solution:
Given Data: Speed of the train = 48$\dfrac{{{\text{km}}}}{{{\text{hr}}}}$ (1km=1000m)
                           = $\dfrac{{48 \times 1000{\text{m}}}}{{1 \times 60{\text{min}}}}$ (1hr=60min)
                           = $800\dfrac{{\text{m}}}{{{\text{min}}}}$

Therefore, in 1minute train crosses 800m.

If the posts are 50m apart. Then, the number of posts in 800m of distance.

Number of posts = $\dfrac{{800}}{{50}}$
  = 16

Hence, there are 16 posts.
Option A is the correct answer.

Note – The key in solving such type of problems is to convert the speed of train into meters per minute and finding the distance travelled in 1minute is important to calculate the number of posts in this distance. We are supposed to know the conversions from km to m and hour to min.