Question

A motorboat goes downstream in a river and covers the distance between two coastal towns in 5 hours it covers this distance upstream in 6 hours if the speed of the stream is 2 kilometre per hour find the speed of the boat in still water

Answer 1

Let the speed of the boat in still water be x.

Given that the speed of the stream is 2km/h.

Upstream:

Speed = ( x - 2) km/h

Distance = Speed x Time

Distance = 6 (x - 2) km

Downstream:

Speed = ( x + 2) km/h

Distance = Speed x Time

Distance = 5(x + 2) km

Solve x:

Since both the distance are the same:

6(x- 2) = 5( x + 2)

6x - 12 = 5x + 10

x = 22 km/h

Answer: The speed of the boat in still water is 22 km/h

Answer 2

Speed = ( x - 2) km/h

Distance = Speed x Time

Distance = 6 (x - 2) km

Downstream:

Speed = ( x + 2) km/h

Distance = Speed x Time

Distance = 5(x + 2) km

Solve x:

Since both the distance are the same:

6(x- 2) = 5( x + 2)

6x - 12 = 5x + 10

x = 22 km/h