Question

A race boat covers a distance of 60 km downstream in one and half hour it covers the distance upstream in 2 hours. the speed of the race boat in still water is 35 km per hour find the speed of the stream.

Answer 1

Answer:

5 km/hr

Explanation:

As the speed of the boat in still water is known to us we can calculate the speed of the stream either any stream i.e. down stream or up stream.
Say, the speed of the stream is x km/hr.
Going downstream the speed of the boat and the speed of the stream will be added together i. e.(35+x) km/hr
Hence the boat goes (35+x) km in 1 hr.
For a distance of 60 km, the Time =6035+xhr
so, 6035+x=112=32
or, 3(35+x)=2⋅60 [cross multiplication]
or, 105+3x=120
or 3x=120−105
or, x=153=5
Speed of the stream is 5 km/hr.
Another way
Going upstream, the speed of the stream is deducted from speed of the boat i.e (35−x)km/hr
Hence goes (35−x) km in 1 hr.
Therefore for a distance of 60 km Time = 6035−xhrs.
As per question, Time is 2 hours, so 6035−x=2
or 60=2(35−x) [ cross multiplication]
or, 60=70−2x
or 2x=70−60
or, x=102=5
So, speed of the stream is 5 km/hr

Answer 2

Let The Speed Of Stream Be x km/hr.

Now Speed Upstream = 35-x

Speed Downstream = 35+x

Now Time = Distance/Speed

3/2 = 60/35+x

And

2 = 60/35-x

Cross Multiplying We Get

105+3x = 120

3x = 15

x = 5

Check By Solving Other Equation

2 = 60/35-x

70-2x = 60

2x = 10

x = 5

So Speed Of Stream = 5km/hr

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