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Asked on November 22, 2019 by

Ashafal Potnuru

The speed of a boat in still water is 8 km/hr It can go 15 km upstream and 22 km downstream in 5 hours. The speed of the stream is ----- km/hr.

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ANSWER

⇒ Let x be the speed of the stream.

⇒ Speed of the boat in still water is 8km/hr

⇒ The speed of the boat in upstream is 8−xkm/hr

⇒ The speed of the boat in downstream is 8+xkm/hr

⇒ The time taken by the boat to cover 15km=

8−x

15

hr

⇒ The time taken by the boat to cover 22km=

8+x

22

hr

According to the question,

⇒

8−x

15

+

8+x

22

=5

⇒ 15(8+x)+22(8−x)=5(8−x)(8+x)

⇒ 120+15x+176−22x=5(64−x

2

)

⇒ 296−7x=320−5x

2

⇒ 5x

2

−7x−24=0

⇒ 5x

2

−15x+8x−24=0

⇒ 5x(x−3)+8(x−3)=0

⇒ (x−3)(5x+8)=0

⇒ x−3=0 and 5x+8=0

⇒ x=3 and x=−

5

8

Speed cannot be negative.

∴ The speed of the stream is 3km/hr

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