Question

A boy goes from his house to school by bus at a speed of 20 km h^-1 and returns back through the same route at a speed of 30 km h^-1. The average speed of his journey is ______.

Options

• 24 km h^-1

•  25 km h^-1

•  30 km h^-1

•  20 km h^-1

Answer 1

A boy goes from his house to school by bus at a speed of 20 km h^-1 and returns back through the same route at a speed of 30 km h^-1. The average speed of his journey is 24 km h^-1.

Explanation:

Let the distance between the school and the house is x km.

speed of the boy from house to school = 20 km/hr.

Using formula, Time taken = `"distance"/"speed"`

So, time taken = `x/20` hours.

Also, Speed of the boy from school to the house = 30 km/hr

So, time taken = `x/30` hours.

Total time taken = `x/20 + x/30 = x/12` hours

Also total distance covered by boy = x + x = 2 x km.

Using formula,

Average speed = `"Total distance"/"Total time"`

`= (2x)/(x/12)`

`= 2cancel(x) xx 12/cancel(x)`

= 24 km/hr.

Thus, average speed of the boy's journey is 24 km h^-1.