Question

• A train travels a distance with a speed of 40 km/h and return with a speed of
60km/h. Calculate the average speed of the train.​

Answer 1

A train travels some distance with a speed of 40 km per hour and returns with a speed of 60 kilometre per hour calculate the average speed of the train.

We have to find the average speed of the train.

Let us assume that the distance covered by the train is 'x' km.

Average speed is defined as the ratio of total distance covered with respect to total time taken.

Total distance covered by the train = (x + x) km = (2x) km

Also,

Time = Distance/Speed

Case 1:

t1 = x/40 hr

Case 2:

t2 = x/60 hr

Total time = t1 + t2= x/40 + x/60

= (3x + 2x)/120

= 5x/120

Therefore,

Average speed of the train = (Total distance covered)/(Total time taken)

= 2x/(5x/120)

= (2x × 120)/5x

= 48 km/hr

Therefore, 48 km/hr is the average speed of the train.

Shortcut Method:

S1 = 40 km/hr and S2 = 60 km/hr

Average speed = (2 × S1 × S2)/(S1 + S2)

= (2 × 40 × 60)/(40 + 60)

= 4800/100

= 48 km/hr

Therefore, 48 km/hr is the average speed of the train.

Answer 2

GIVEN:

• Train travelling with a speed of 40km/h
• Returning with a speed of 40km/h

TO FIND:

• Average speed of train

SOLUTION:

Let

• Distance travelled : x
• Returning distance : x
• Total distance : x + x = 2x

Using

Time = distance/speed

→ Time = x/40 + x/60

→ Time = 5x/120

Finding the average speed

→ Avg. speed = Total distance/Total time

→ Avg. speed = 2x/5x/120

→ Avg. speed = 240/5

→ Avg. speed = 48 km/h

.°. Hence, average speed = 48km/h