Question

Speed of a boat in still water is 15 km/h. it goes 30 km upstream and returns back at the same point in 4 hours 30 minutes. find the speed of the stream.

Answer 1

speed of stream = x km/h
speed upstream = 15-x km/h
speed downstream = 15+x km/h
30/(15-x) + 30/(15+x) =4.5 =9/2
(15+x +15-x)/(15²-x²) =9/2 (1/30)
30/(225-x²) = 9/60
1/(225-x²) = 9/60 (1/30) =1/200
225-x² = 200
x² = 25
x= +5 or x =-5 km/h

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!