Question 19

The respective ratio between the time taken by a boat to travel the same distance downstream in stream A and that in stream B is 8 : 7. The speed of the boat is 12 km/h and the speed of stream A is half the speed of stream B. What is the speed of stream B ? (in km/h)

Solution

Let speed of stream B = $$2x$$ km/h

and speed of stream A = $$x$$ km/h

Speed of stream = $$12$$ km/h

Acc to ques,

=> $$\frac{\frac{1}{12 + x}}{\frac{1}{12 + 2x}} = \frac{8}{7}$$

=> $$\frac{12 + 2x}{12 + x} = \frac{8}{7}$$

=> $$84 + 14x = 96 + 8x$$

=> $$14x - 8x = 96 - 84$$

=> $$x = \frac{12}{6} = 2$$

$$\therefore$$ Speed of stream B = $$2 \times 2 = 4$$ km/h

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