Question

Snehal can row $28km$ downstream and $12km$ upstream in 5 hours. He can row $21km$ downstream and $10km$ upstream in 4 hours. Find the speed of Snehal in still water.

• A. $9kmph$
• B. $8kmph$
• C. $6kmph$
• D. $5kmph$

Answer 1

Answer: (A)

Let Snehal's speed and the speed of the stream be $x$ kmph and $y$ kmph, respectively.
Given, $\frac{28}{x+y}+\frac{12}{x-y}=5$
and, $\frac{21}{x+y}+\frac{10}{x-y}=4$
Let $\frac{1}{x+y}=a$ and $\frac{1}{x-y}=b$, then
Eq. (1) $\Rightarrow 28a+12b=5$
and Eq. (2) $\Rightarrow 21a+10b=4$
Solving Eqs. (3) and (4), we get,
$a=\frac{1}{14}$ and $b=\frac{1}{4}$
$\Rightarrow x+y=14$ and $x-y=4$
$\Rightarrow x=9$ and $y=5$
$\therefore$ Snehal's speed in still water $=9kmph$