Question

A motorcyclist drives from place A to B with a uniform speed of 30 km/h and return from place B to A with a uniform speed of 20 km/h.Find its average speed. Sir / mam i don't understand from where 2 ×30× 30 / 20+ 30 it is written?

Answer 1

Answer:

Let distance between A and B is D

Then, time taken by motorcyclist with uniform speed 30 km/h ,T₁ = distance/speed = D/30 hrs

Again, they return with uniform speed 20 km , so time taken by motorcyclist , T₂ = D/20 hrs

Now, average speed of motorcyclist = total distance/total time taken

= (D + D )/(D/30 + D/20) km/h

= 2 × 30 × 20/(30 + 20) km/h

= 24 km/h