Question 29

A man can row threequarters of a kilometre against the stream in 45/4 min and return in 15/2 min. The speed of the man in still water is :

Solution

$$speed = \frac{distance}{time}$$

=> Upstream speed = $$\frac{\frac{3}{4}}{\frac{45}{4} \times \frac{1}{60}}$$

= $$\frac{3 \times 60}{45} = 4$$ km/h

Downstream speed = $$\frac{\frac{3}{4}}{\frac{15}{2} \times \frac{1}{60}}$$

= $$\frac{3 \times 2 \times 60}{15 \times 4} = 6$$ km/h

$$\therefore$$ Speed of man in still water = $$\frac{1}{2}$$ (downstream + upstream)

= $$\frac{1}{2} (6 + 4)$$

= $$\frac{10}{2} = 5$$ km/h

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A man can row three­quarters of a kilometre against the stream in 45/4 min and return in 15/2 min. The speed of the man in still water is :