Question 64

A boat can travel 21 km in 3 hours going upstream. It can travel 55 km in 5 hours going downstream. What is the speed of the stream?

Solution

Let's assume the speed of the boat in still water and the speed of the stream are 'B' and 'C' respectively.

A boat can travel 21 km in 3 hours going upstream.

$$B-C\ =\ \frac{21}{3}$$

B-C = 7 km/h Eq.(i)

It can travel 55 km in 5 hours going downstream.

$$B+C\ =\ \frac{55}{5}$$

B+C = 11 km/h Eq.(ii)

So Eq.(ii)-Eq.(i) ==> B+C-(B-C) = 11-7

B+C-B+C = 4

2C = 4

Speed of the stream = C = 2 km/h

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