Question

A motorboat goes downstream in the river and covers the distance between two coastaltown in 3 hours. It covers this distance upstream in 4 hours. If the speed of the stream is5 km/hr, find the speed of the boat in still water and the distance between the twocoastal towns.

Answer 1

we have the following:

speed of the boat in still water be x

the speed of the stream is 5 km/h

upstream

$\begin{gathered} speed=x-5 \\ d=s\cdot t \\ d=(x-5)\cdot4 \\ \end{gathered}$

downstream:

$\begin{gathered} speed=x+5 \\ d=s\cdot t \\ d=(x+5)\cdot3 \\ \end{gathered}$

therefore:

$\begin{gathered} (x-5)\cdot4=(x+5)\cdot3 \\ 4x-20=3x+15 \\ 4x-3x=15+20 \\ x=35 \end{gathered}$

The answer is 35 km/h