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

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Solution

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 $= \frac{d i s t a n c e}{s p e e d} .$
So, time taken $= \frac{x}{20}$ hours.
Also,Speed of the boy from school to the house $= 30$ km/hr
So, time taken $= \frac{x}{30}$ hours.
Total time taken $= \frac{x}{20} + \frac{x}{30} = \frac{x}{12}$ hours
Also total distance covered by boy $= x + x = 2 x$ km.
Using formula,
Average speed $= \frac{T o t a l d i s t a n c e}{T o t a l t i m e} = \frac{2 x}{\frac{x}{12}} = 24$ km/hr.
Thus, average speed of the boy's journey is $24$ km/hr.

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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:

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