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In a river, the ratio of the speed of stream and speed of the boat in still water is 4 : 7. Again, the ratio of the speed of the stream and speed of another boat in still water is 2 : 5. What is the ratio of the speed of the first boat to the second boat in still water?

In a river, the ratio of the speed of stream and speed of the boat in still water is 4 : 7. Again, the ratio of the speed of the stream and speed of another boat in still water is 2 : 5. What is the ratio of the speed of the first boat to the second boat in still water? Correct Answer 7 : 10

Given:

For the first boat,

Speed of stream : speed of the boat in still water = 4 : 7

Let the speed of the stream be 4x km/hr and speed of boat in still water be 7x km/hr

For the second boat,

Speed of stream : speed of the boat in still water = 2 : 5

Let the speed of the stream be 2y km/hr and speed of the boat in still water be 5y km/hr

Formula used:

Speed of the boat in still water = (Downstream speed + Upstream speed)/2

Speed of stream = (Downstream speed – Upstream speed)/2

Calculation:

In both the conditions, the river is the same

⇒ 4x = 2y

⇒ x = y/2

∴  Required ratio = 7x  :  5y

⇒ (7 × y/2) : 5y

⇒ 7  : 10

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