Question

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 4 hour 30 minutes. Find the speed of the stream

Answer 1

The speed of the boat in still water is 15km/hr.It can go 30 km upstream and return to down stream in 41/2hrs.find the speed of the stream.

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let x=speed of stream

(15+x)=speed of boat downstream

(15-x)=speed of boat upstream

travel time=distance/speed

30/(15+x)+30/(15-x)=9/2

60/(15+x)+60/(15-x)=9

LCD: (15+x)(15-x)

60(15-x)+60(15+x)=9(15+x)(15-x)

60(15-x+15+x)=9(225-x^2)

60(30)=2025-9x2

9x^2=2025-1800

9x2=225

take sqrt of both sides

3x=15

x=5

speed of stream=5 km/hr

Answer 2

Hey there!

Let speed of stream = x km/h

∴ Downstream speed = (15+x) km/h

∴ Upstream speed = (15-x) km/h

∴ 30/(15+x) + 30/(15-x) = 4 1/2

→ 900/225-x² = 9/2

→ 9x² = 225

→ x² = 25

→ x = 5

∴ Speed of stream = 5 km/h

Hope it Helps You!