Multiple choice

In a river, the ratio of the speed of stream and speed of a boat A in still water is 2 : 5. Again, in the same river ratio of the speed of stream and speed of an another boat B in still water is 3 : 4. What is the ratio of the speeds of the boat A to the boat B in still water ?(if speed of stream is same in both conditions.)

  1. 10 : 7

  2. 15 : 8

  3. 4 : 3

  4. 5 : 4
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let S be the speed of the stream. Boat A: S/A = 2/5 -> A = 2.5S. Boat B: S/B = 3/4 -> B = (4/3)S. The ratio A:B = 2.5S : (4/3)S = 2.5 : 1.333 = 7.5 : 4 = 15 : 8.

AI explanation

To compare the boats, we first equalize the speed of the stream by making the stream value 6 in both ratios, which changes the ratio for boat A to 6:15 and keeps the ratio for boat B at 6:8. We then directly compare the still water speeds of boat A and boat B. This yields the ratio 15 to 8 for the speeds of boat A to boat B in still water.

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