Miscellaneous Question 54
- A boat takes 630 minutes to travel from point $A$ to $B$ and then come back to point $A$. The distance between point $A$ and $B$ is $72$ $ km$. If the respective ratio of speed of the boat in still water and speed of water current is 7 : 1 , what is the speed of the boat downstream? (in $kmph$ )
(1) 23
(2) 12
(3) 24
(4) 16
(5) 8
(IBPS Bank PO/MT CWE (Prelim Exam) 14.10.2018)
Show Answer
Correct Answer: 54. (4)
Solution: 54. (4) $\mathrm{AB}=72$ $ \mathrm{km}$.
Total time $=630$ minutes
$=\left(\frac{630}{60}\right)$ hours $=\frac{21}{2}$ hours
Speed of boat in still water $=7 x $ $\mathrm{kmph}$
Speed of current $=x $ $\mathrm{kmph}$.
Rate downstream $=8 x $ $\mathrm{kmph}$.
Rate upstream $=6 x $ $\mathrm{kmph}$
According to the question,
$\frac{72}{8 x}+\frac{72}{6 x}=\frac{21}{2}$
$\Rightarrow \frac{9}{x}+\frac{12}{x}=\frac{21}{2}$
$\Rightarrow \frac{21}{x}=\frac{21}{2} \Rightarrow x=\frac{21 \times 2}{21}$
$=2$ $ \mathrm{kmph}$.
$\therefore$ Rate downstream $=8 x$
$=(8 \times 2)$ $ \mathrm{kmph}$.
$=16 $ $\mathrm{kmph}$
BETA
