Abdul, while driving to school, computes the average speed from his trip to be $20 km / h$ . On his return trip along the same route, there is less traffic and the average speed is $40 km / h$ . What is the average speed for Abdul’s trip?

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26.67 km / h

28.5 km / h

32.67 km / h

35 km / h

answer is A.

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Detailed Solution

The average speed for Abdul’s trip is

26.67 km / h

Given:

V = 20 km / h, v = 40 km / h

Let the distance between Abdul’s home to his school be

S

.
Time taken to reach the school

= \frac{S}{V} = \frac{S}{20} h

Time taken to reach home from the school

= \frac{S}{V} = \frac{S}{40} h

Therefore, time taken to complete the trip

= \frac{S}{20} + \frac{S}{40}

= \frac{3 S}{40} h

Total distance travelled during the trip

= 2 S

Therefore, average speed for Abdul’s trip

= \frac{2 S}{3 S} \times 40

= 26.67 km / h

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