Question

A boat whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is: 4,5,6 or 10

Answer 1

Sol:

let speed of stream be x ( km/hr)

Therefore

Downstream = x + 15km/hr

upstream = x - 15km/hr

as t = d/v

According to the given condition,,

Time taken downstream + time taken upstream = 4.5 hour ,,

(30/x + 15) + (30/x - 15) = 4.5

multiplying both the side of equations by 2(x + 15) (x - 15)

we get

9( 15² - x²) = 60(15 - x) + 60(15 + x) = 1800

dividing both the side of equation by 9

225 - x² = 200

Adding x² - 200to both the side of equation.

25 = x² , x = 5

➡️➡️Speed of stream is 5km/hr