Question

A boat travels 88 kms downstream and 65 km upstream in 9 hours while it travels 121 km downstream and 97.5 km upstream in 13 hours. Find the speed of stream(in km/hr).

1. 1.5
2. 2.5
3. 3.5
4. 4.5
5. 5.5

Answer 1

Correct Answer - Option 4 : 4.5

Given:-

Time for 88 kms downstream and 65 km upstream = 9 hours

Time for 121 kms downstream and 97.5 km upstream = 13 hours

Formula:-

Speed = Distance/Time

Downstream speed = u + v

Upstream speed = u - v

Boat speed = ½ (D + U)

Stream speed = ½ (D - U)

U and v are boat and stream speeds and D and U downstream and upstream speeds.

Calculation:-

88/(u + v) + 65/(u - v) = 9

121/(u + v) + 97.5/(u - v) = 13

Let 1/(u + v) = x and 1/(u - v) = y

88x + 65y = 9

121x + 97.5y = 13

Solving both, x = 1/22 and y = 1/13

Or U = 13 and D = 22

V = ½ (22 – 13) = 4.5 km/hr