Question

A train travels some distance with a speed of 30 km/ h and returns with a speed of 45 km/h. Calculate the average speed of the train

Answer 1

Explanation:

let the distance of the train be x.

case 1) speed = 30 km/h

distance = x

time = distance/ speed

= x/ 30

case 2) speed = 45 km/h

distance= x

time = x/45

case 3)

$average \: speed \: = \frac{total \: distance \: }{total \: time}$

total distance = x+x = 2x

$total \: time \: = \frac{x}{30} + \frac{x}{45}$

$\frac{ 3x}{90} + \frac{2x}{90} = \frac{5x}{90}$

$average \: speed \: = \frac{2x}{5x} \times 90$

$= 2 \times 18$

$= 36$

hence, the average speed of the train is 36 km/h