A B and C are situated at the bank of river which is flowing at a constant rate B is at an equal dis...........

Quant (SSC) Boats and Streams

A, B and C are situated at the bank of river which is flowing at a constant rate. B is at an equal distance with A and C. A swimmer avinash takes 10 h to swim from A to B and B to A .Also, he takes 4 h to swim from A to C. What is the ratio of speed of Avinash is still water and speed of stream?

5 : 3

3 : 5

2 : 5

1 : 2

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Explanation:

Let speed of Avinash in still water = a km/h
and speed of stream = b km/h
Let AB = BC = x km
From first condition,
x / (a + b) + x /(a - b) = 10 .......(i)
From second condition,
2x /a + b = 4
⇒ x /a + b = 2 .......(ii)
From Eqn. (i) and (ii) , we get
2 + x /a - b = 10
⇒ x /(a - b) = 8 ... (iii)
From Eqn. (ii) and (iii), we get,
a + b /a - b = 8/2 = 4
⇒ a + b = 4a – 4b
⇒ 3a = 5b
⇒ a : b = 5 : 3