Miscellaneous Question 72
- A boat takes six hours to travel a certain distance downstream and five hours to travel a certain distance upstream. The distance travelled upstream is half of the distance travelled downstream. If the speed of the current is $4 $ $km /hr$, what is the speed of the boat in still water? (in $km / hr$ )
(1) 16
(2) 20
(3) 24
(4) 10
(5) 18
(IBPS Specialist Officer CWE (Prelim Exam) 31.01.2019)
Show Answer
Correct Answer: 72. (1)
Solution: 72. (1) Speed of boat in still water = $x$ kmph.
$\therefore$ Rate downstream
$=(x+4) $ $\mathrm{kmph}$.
Rate upstream
$=(x-4) $ $\mathrm{kmph}$
Distance covered in upstream $=$ $y \mathrm{km}$.
$\therefore \frac{2 y}{x+4}=6$
$\Rightarrow \frac{y}{x+4}=3$
$\Rightarrow y=3(x+4) $ …. (i)
Again,
$\frac{y}{x-4}=5$
$\Rightarrow y=5(x-4)$ …. (ii)
$\therefore 5(x-4)=3(x+4)$
$\Rightarrow 5 x-20=3 x+12$
$\Rightarrow 5 x-3 x=20+12$
$\Rightarrow 2 x=32 $
$\Rightarrow x=16$ $ \mathrm{kmph}$.
BETA
