Miscellaneous Question 11
- The respective ratio between speed of the boat upstream and speed of the boat downstream is $3: 4$. What is the speed of the boat in still water if it covers 70 $km$ downstream in 3 hours 30 minutes? (in $km / h$ )
(1) 18
(2) 18.5
(3) 17
(4) 17.5
(5) 16
(IBPS Bank PO/MT CWE-V (Preliminary) 04.10.2015)
Show Answer
Correct Answer: 11. (4)
Solution: 11. (4) Rate downstream
$=4 x $ $\mathrm{kmph}$
Rate upstream $=3 x $ $\mathrm{kmph}$
According to the question,
Time $=\frac{\text { Distance }}{\text { Speed }} ; \frac{70}{4 x}=3 \frac{1}{2}$
$\Rightarrow \frac{70}{4 x}=\frac{7}{2} \Rightarrow \frac{10}{2 x}=1$
$\Rightarrow 2 x=10 \Rightarrow x=5$
$\therefore \quad$ Rate upstream $=5 \times 3$
$=15$ $ \mathrm{kmph}$
Rate downstream $=5 \times 4$
$=20 $ $\mathrm{kmph}$
$\therefore \quad$ Speed of boat in still water
$=\frac{1}{2}(20+15) $ $\mathrm{kmph}$
$=\frac{35}{2}=17.5 $ $\mathrm{kmph}$
BETA
