Question

A man can row 18 km/hr in still water. It takes him thrice as long to row up as to row down the river. Find the rate of stream.

Answer 1

Answer:

9 km/hr

Step-by-step explanation:

Given A man can row 18 km/hr in still water. It takes him thrice as long to row up as to row down the river. Find the rate of stream.

Let man can row p km / hr up the river.

So he rows 3 p km down the river.

Now rate of water is 3 p + p = 4 p and in still water is 1/2 x 4 p = 2 p km / h

So 2 p = 18

  p = 9 km / hr is rate of up the river and 9 x 3 = 27 km / hr is rate of down the river.

Now we need to find rate of stream which is

1/2 x (27 - 9)

1/2 x 18

9 km / hr

So rate of stream will be 9 km / hr

Answer 2

Answer:

9 km/Hr

Step-by-step explanation:

A man can row 18 km/hr in still water. It takes him thrice as long to row up as to row down the river. Find the rate of stream.

Let say distance = D km

Speed of Stream = S km/Hr

Upstream speed (row up) = 18 - S km/Hr

Upstream Time = D/(18-S)

Downstream speed (row up) = 18 + S km/Hr

Downstream Time = D/(18+S)

Upstream Time = 3 * Downstream Time

=> D/(18-S) = 3 * D/(18+S)

=> 18 + S = 54 - 3S

=> 4S = 36

=> S = 9

the rate of stream = 9 km/Hr