A man takes 2.2 times as long to row a distance upstream as to row the same distance downstream. If he can row 55 km downstream in 2 hour 30 minutes, what is the speed of the boat in the still water?

140 km/h
28 km/h
316 km/h
424 km/h

Answer:- 1

Explanation:-

Solution:

\begin{aligned} Speed of the boat in downstream \\ = \frac{55}{2.5} = \frac{55 \times 10}{2.5} = 22 k m / h r \\ Then, speed of the boat in upstream \\ = \frac{22}{2.2} = \frac{22 \times 10}{22} = 10 k m / h r \\ ∴ Speed of the boat in still water \\ = \frac{22 + 10}{2} = 16 k m / h r \end{aligned}

$\eqalign{ & {\text{Speed of the boat in downstream }} \cr & {\text{ = }}\frac{{55}}{{2.5}} = \frac{{55 \times 10}}{{2.5}} = 22\,km/hr \cr & {\text{Then, speed of the boat in upstream}} \cr & {\text{ = }}\frac{{22}}{{2.2}} = \frac{{22 \times 10}}{{22}} = 10\,km/hr \cr & \therefore {\text{Speed of the boat in still water}} \cr & {\text{ = }}\frac{{22 + 10}}{2} = 16\,km/hr \cr}$