Question

A man can row a boat at the rate of 4km/hr in still water it takes 2 hours more to row the boat 6km upstream

Answer 1

Step-by-step explanation:

Let the stream be flowing at s km/hr.

When rowing upstream, the boat moves at (4-s) km/hr.

When rowing downstream, the boat moves at (4+s) km/hr.

The time taken to row 2 km upstream = 2/(4-s) hr.

The time taken to row 2 km downstream = 2/(4+s) hr.

The total time taken to row both upstream and downstream = 2 hrs. Hence

2/(4-s) + 2/(4+s) = 2, or

1/(4-s) + 1/(4+s) = 1, or

4+s+4-s = (4-s)(4+s), or

8 = 16-s^2, or

s^2 = 8, or

s = 2√2

The stream flows at 2√2 km/hr.

Check: 2/(4-2√2 ) +2/(4+2√2) = 1.707106781 + 0.292893218 = 2. Correct.