Question

A motor boat, travelling at the same speed, can cover 25 km upstream and 39 km downstream in 8 hours. At the same speed, it can travel 35 km upstream and 52 km downstream in 11 hours. The speed of the stream is​

Answer 1

Answer:

Let the speed of a boat and stream be x and y km/h.

Therefore, Speed of boat along stream = (x + y) km/h

and speed of boat against stream = (x - y) km/h

According to the question,

25x−y+39x+y=8 ...(i)

and 35x−y+52x+y=11 ...(ii)

On multiplying Eq. (i) by 4 and Eq. (ii) by 3,

then subtract Eq. (ii) from Eq. (i), we get

100x−y−105x−y=1

5x−y=1

x - y = 5 ...(iii)

On substituting the value of (x y = 5) in Eq. (i), we get

255+39x+y=8

39x+y=8−5

x+y=393

x+y=13 ...(iv)

On solving Eqs. (iii) and (iv), we get

x = 9

and y = 4

Hence, speed of stream = 4 km/h

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