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In a stream, the ratio of the speed of the boat in still water and the speed of the stream is 7 : 5. The ratio of the speed of another boat in still water to the speed of the stream is 4 : 3. What is the ratio of the speed of the second boat to that of the first boat in still water?

In a stream, the ratio of the speed of the boat in still water and the speed of the stream is 7 : 5. The ratio of the speed of another boat in still water to the speed of the stream is 4 : 3. What is the ratio of the speed of the second boat to that of the first boat in still water? Correct Answer 20 : 21

Given:

Ratio of speed of 1st boat in still water and speed of stream = 7 : 5

Ratio of speed of 2nd boat in still water and speed of stream = 4 : 3

Calculation:

For the first boat let the speed of the stream be 5x and the speed of the boat be 7x.

For the 2nd boat, let the speed of the stream be 3y and the speed of the 2nd boat be 4y.

The speed of the stream will be the same.

∴ 5x = 3y

⇒ x = 3y/5

Now, the required ratio of the speed of the second boat to that of the first boat = 4y : 7x

⇒ 4y : 7 × (3y/5)

⇒ 20y : 21y

⇒ 20 : 21

∴ The ratio of the speed of the second boat to that of the first boat in still water is 20 : 21.

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