A race boat covers a distance of 60 km downstream in one and a half hours. It covers this distance upstream in 2 hours. The speed of the race boat in still water is 35 km/hr. find the speed of the stream.

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5 km / hr

5 m / s

0.5 km / s

6 km / m

answer is A.

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Detailed Solution

Suppose, speed of stream = x km/hr
Speed of boat in still water = 35 km/hr
In downstream speed of boat
= (35+x) km/hr
Now, we know that,
Time = distance /speed
So time taken to cover 60 km distance
Time

= \frac{60}{35 + x} hr

Now, Time taken to cover this distance is one and half hour. So,

1 \frac{1}{2} = \frac{60}{35 + x}

\frac{3}{2} = \frac{60}{35 + x}

3 (35 + x) = 2 \cdot 60

105 + 3 x = 120

3 x = 120 - 105

x = \frac{15}{3} = 5

So, speed of the stream = 5 km/hr.
Correct option is 1.

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