Question

ANSWER IT CORRECTLY

The speed of a boat in still water is 15 km/hr. It can go 30 km upstream and return downstream to the original point in 7 hours 12 minutes. Find the speed of the stream.


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Answer 1

Answer:

Given :

Speed of boat in still water =15 km/hr

Let x be speed of the stream in km/hr

Speed of the boat upstream =15−x

Speed of the boat down stream =15+x

Time taken for upstream T

1

=

15−x

30

Time taken for downstream T

2

=

15+x

30

Given, T

1

+T

2

=

2

9

=

15−x

30

+

15+x

30

=

2

9

=30(

15−x

1

+

15+x

1

)=

2

9

=30(

(15−x)(15+x)

15+x÷15−x

)=

2

9

=

225−x

2

30×30

=

2

9

=

225−x

2

100

=

2

1

⇒225−x

2

=200

⇒x

2

=25

⇒x=5 ....(∵x is +ve)

⇒x=5 km/hr

Speed of the stream =5 km/hr.

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