| In a river, the ratio of the speed of stream and speed of a boat in still water is 2 : 5, Again, ratio of the speed of stream and speed of an another boat in still water is 3 : 4. What is the ratio of the speeds of the first boat to the second boat in still water? |
A) 10 : 7
B) 15 ; 8
C) 4 : 3
D) 5 : 4
E) None of these
Correct Answer: D
Solution :
| For the first boat, |
| Speed of stream: Speed of boat = 2: 5 |
| Let speed of stream be2 x km/h and speed of boat be 5x km/h. |
| Similarly, for the second boat |
| Speed of stream: Speed of boat = 3: 4 |
| Let speed of stream be 3y km/h and speed of boat be 4y. |
| In both of the conditions, river is same |
| \[\therefore \]\[2x=3y\]\[\Rightarrow \]\[x=\frac{3}{2}\,\,y\] |
| Thus, required ratio in speeds of boats in still water |
| \[=5x:4y=5\times \frac{3}{2}y:4y=15:8\] |
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