Trains Boats and Streams Practice Test 4 with solutions

Question : 24 of 40

Marks: +1, -0

A motor boat can travel at 10 km/hour in the still water. It travels 91 km downstream and comes back in 20 hours. Find the rate of flow of the river.

Solution:

{91}/{10+x}+{91}/{10-x}

= 20

{10-x+10+x}/{100-x^2}

{20}/{91}

x^2

- 9 = 0
x = ±3
x = 3 km/hour

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