Question

The speed of a boat in still water is 8 km/hr. It can go 15 km upstream and 20 km downstream in 5 hr. Find the speed of the stream.
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Class 10 - Math - Quadratic Equation
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Answer 1

Answer:

Hii

Step-by-step explanation:

⇒ 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+x22

hr

According to the question,

⇒ 8−x

15 + 8+x22

=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=− 58

Speed cannot be negative.

∴ The speed of the stream is 3km/hr

I hope it helps you