Question

A person goes from A to B at the speed of 40 kmph and comes back at the speed of 60 kmph. What is his average speed for the whole journey?

Answer 1

Answer: 48 km/hr

Step-by-step explanation:

Speed of the person from A to B = 40 km/hr

Speed of the person from B to A = 60 km/hr

 

There are two methods by which we can find the average speed for the whole journey:

Method 1:  shortcut method

Since the person covers an equal distance for the forward & return journey, therefore, by using the formula, we get

Average Speed = $\frac{2xy}{x+y}$

where

x = 60 km/hr & y = 40 km/hr  

∴ Average Speed = (2*60*40) / (60+40) = 4800/100 = 48 km/hr

Method 2:  explained method

Let the distance covered by the person from A to B be “x” km.

So, the total distance = 2x km

Now,

The time taken for the forward journey from A to B = (x/60) hr  

The time taken for the return journey from B to A = (x/40) hr

∴ The total time = x/60 + x/40 = [(100x)/2400] hr

Thus,

Average speed  

= [Total distance] / [Total Time]

= [2x] / [100x/2400]

= 48 km/h