Question 57

A man travels from P to Q at the speed of 60 km/h and travels from Q to P at the speed of 90 km/h. What is the average speed of the man for the whole journey?

Solution

Let's assume the distance between P and Q is 'd' km.

A man travels from P to Q at the speed of 60 km/h and travels from Q to P at the speed of 90 km/h.

the average speed of the man for the whole journey = $$\frac{\left(d+d\right)}{\frac{d}{60}+\frac{d}{90}}$$

= $$\frac{2d}{\frac{3d}{180}+\frac{2d}{180}}$$

= $$\frac{2d}{\frac{5d}{180}}$$

= $$\frac{2\times\ 180}{5}$$

= 72 km/h

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