3. Abdul, while driving to school, computes the average speed for
his trip to be 20 km h-!. On his return trip along the same
route, there is less traffic and the average speed is
30 km hl. What is the average speed for Abdul's trip?
Answers
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Correct Question -
Abdul while driving to school computes the average speed of the trip to be 20 kmph .
On his return trip along the same route , there is less traffic and the average speed is 30 kmph .
What is the average speed for Abdul ' s trip ?
Solution -
See the attached diagram ....
In the above Question , the following information is given -
Abdul while driving to school computes the average speed of the trip to be 20 kmph .
On his return trip along the same route , there is less traffic and the average speed is 30 kmph .
So ,
The innitial average speed is 20 kmph .
The final average speed is 30 kmph .
Let the distance between Abdul ' s home and his school be D metres .
Total distance covered by Abdul = 2 D
We also know the following formula -
Speed = [ Total Distance Covered ] / [ Total time taken ]
So ,
20 = [ D ] / [ T 1 ]
=> T 1 = [ D ] / 20
30 = [ D] / [ T 2 ]
=> T2 = [ D ] / 30
Total time taken for the whole trip
=> T 1 + T 2
=> D / 20 + D / 30
=> ( 5 D ) / 60
Now , Similarly -
Average Speed = [ Total Distance Covered ] / [ Total time taken ]
=> Average speed
=> [ 2 D ] / [ ( 5 D / 60 )
=> 24 kmph .
Hence the average speed for Abdul ' s trip is 24 kmph ...
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