| A boat running upstream takes 5 h 12 min to cover a certain distance, while it takes 4 h to cover the same distance running downstream. What is the ratio between the speed of the boat and speed of the water in current respectively? |
A) 23 : 3
B) 21: 2
C) 25 : 7
D) 28 : 9
Correct Answer: A
Solution :
(a) Let the boat upstream speed be x km/h and that downstream be y km/h. Then, distance covered upstream in 5 h 12 min. \[\Rightarrow \]\[\left( x\times \frac{26}{5} \right)=y\times 4\]\[\Rightarrow \]\[y=\frac{13x}{10}\] \[\therefore \]Required ratio \[=\left( \frac{y+x}{2} \right):\left( \frac{y-x}{2} \right)\]\[=(y+x):(y-x)\] \[=\left( \frac{13x}{10}+x \right):\left( \frac{13x}{10}-x \right)\] \[=\frac{23}{10}:\frac{3}{10}=23:3\]
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