Question

Abdul while driving to school computes the average speed for his trip be 20km/h on his return trip along the same route there is lees traffic and the average speed 30km/h what is the average speed foe abdul trip?

Answer 1

Hi dear,

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Let the distance from Abdul's house to school is ' D ' and time taken to reach from home to school is ' T ' and that of coming from school to house it ' t '.

According to question,

For going home to school,

Total distance / Total time taken to cover that distance = average speed

We have , total distance = D and total time taken = T.

So,  D / T = 20 km/h

       T = Dh / 20 km.     ----------------------------- eq.1

Now from coming from school to home,

We have, 

total distance = D and time taken = t.

Total distance / Total time taken to cover that distance = Average speed

D / t = 30 km/h

t = Dh / 30 km.             -------------------------------- eq.2

Now, for his average speed for total journey,

Total distance = D + D = 2D.

Total time taken = T + t.

Average speed = Total distance / total time taken to cover that distance

                         = 2D / ( T + t )       ------------------ eq.3

By putting the value of eq.1 and eq.2 in eq.3,

                          = 2D / ( Dh / 20 km + Dh / 30 km )


                                         3Dh + 2Dh
                          = 2D / ( -------------------- )
                                             60 km


                          = 2D / ( 5 Dh / 60 km )

                          = 2D * 60 km / 5Dh

                          = 24 km/h.