Question

a train cover a certain distance at a speed of 20 km/hr and return back through the same distance at a speed of 30 km/hr. what is the average speed of the train for the whole journey ​

Answer 1

In 1st case

speed=20km/hr

Let distance=x and time=t1

.°. Speed=Distance÷Time

So,20=x/t1

t1=x/20

In 2nd case

speed=30km/hr

Let distance=x and time=t2

.°.speed=distance÷time

So,30=x/t2

t2=x/30

Therefore,total distance=(x+x)km =(2x)km

Total time taken =(x/20+x/30)hr

=(3x+2x/60)hr = (5x/60)hr = x/12 hr

So,average speed =(2x.12/x)km/hr

=24km/hr

Answer 2

Pl see the attached file