Question

Amotar boat whose speed is 15 km/h in still water goes 30 km downstream and come backs in a total time of 4 hours 30 minutes .find the speed of the stream

Answer 1

Speed of the boat = 15 km/h

Let the speed of the stream be x km/h

Upstream:

Speed = (15 - x) km/h

Distance = 30 km

Time = Distance ÷ Speed

Time = 30 / ( 15 - x)

Downstream:

Speed = (15 + x) km/h

Distance = 30 km

Time = Distance ÷ Speed

Time = 30 / ( 15 + x)

Solve x:

Total time = 4 hours 30 min = 4.5 hour

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

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

450 + 30x + 450 - 30x = 4.5(15² - x²)

900 = 1012.5 - 4.5x²

4.5x² = 1012.5 - 900

4.5x² = 112.5

x² = 25

x = √25

x = 5 km/h

Answer: The speed of the stream is 5 km/h