Question

a car can travel form A to B at a speed of 20km/hr and returns at a speed of 30km/hr.The average speed of the car for the whole journey is

Answer 1

the average speed is 25km/hr

Answer 2

Total average speed of car = total distance/ total time taken.

Let D the fistance travelled by each car in each direction.

Time spent on onward trip = t1
Time spent on return trip = t2
Total distanve travelled by car = D +D = 2D

Speed = distance/time

S1 = D/t1
t1 = D/S1

S2 = D/t2
t2 = D/S2

Total average speed = Total distance/ Total time = 2D/( t1 + t2) = 2D/(D/S1 + D/S2)

= 2S1 × S2 / S1 + S2

So average speed = 2× 20 × 30 / 20 + 30
1200 / 50 = 24

So average speed = 24 km / hr

Hope it helps.

And best of luck!!!!