## The speed of the boat in still water is 15 km/hr.It can go 45 km upstream and return downstream to original point in 6 hours and 45 minutes.

Question

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## Answers ( )

Answer: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.

Answer:## Speed of stream = 15 km/hr. Hence upstream speed = 60 – 15 = 45 km/hr. So time taken to cover 20 km = 20/45*60 = 26.67min.

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