Question

The speed of boat in still water is 15 km/h. It can go 30 km downstream and return back to its original point in 4 hrs 30 min. Find the speed of
the stream.

Answer 1

let speed of stream is x kmph
$\frac{30}{15 + x} + \frac{30}{15 - x} = \frac{9}{2} \\ \frac{30(15 - x) + 30(15 + x)}{225 - {x}^{2} } = \frac{9}{2} \\ \frac{450 - 30x + 450 + 30x}{225 - {x}^{2} } = \frac{9}{2} \\ 2(900) = 9(225 - {x}^{2} ) \\ 2(100) = 225 - {x}^{2} \\ \\ 200 - 225 = - {x}^{2} \\ - 25 = - {x}^{2} \\ {x}^{2} = 25 \\ x = \sqrt{25} \\ x = 5$
speed of stream 5 kmph

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!