Miscellaneous Question 51
- The difference between downstream speed and upstream speed of boat $6$ $ km / hr$ and boat travels $72$ $ km$ from $P$ to $Q$ (downstream) in 4 hours. Find the speed of boat in still water.
(1) $15 $ $km / hr$
(2) $18$ $ km / hr$
(3) $20$ $ km / hr$
(4) $80$ $ km / hr$
(5) $24$ $ km / hr$
(IBPS RRBs Officer CWE (Prelim Exam) 18.08.2018)
Show Answer
Correct Answer: 51. (1)
Solution: 51. (1) Speed of boat in still water $=$ $x$ kmph
Speed of current $=y $ $\mathrm{kmph}$
Rate downstream $=(x+y) $ $\mathrm{kmph}$
Rate upstream $=(x-y) $ $\mathrm{kmph}$
According to the question,
$(x+y)-(x-y)=6$
$\Rightarrow 2 y=6$
$\Rightarrow y=3$ $ \mathrm{kmph}$
$\therefore$ Rate downstream of boat
$=\frac{72}{4}=18 $ $\mathrm{kmph}$
$\therefore x+y=18$
$\Rightarrow x+3=18$
$\Rightarrow x=18-3=15 $ $\mathrm{kmph}$
BETA
