Question

Downstream speed is 66.67% more than upstream speed. Speed of boat in still water is 8 km/hr. Find time(in hours) required for boat to cover a round trip of 120 km (60 km each side)

1. 12
2. 15
3. 18
4. 20
5. 16

Answer 1

Correct Answer - Option 5 : 16

Given:-

Speed of boat in still water, u = 8 km/hr

Formula:-

Speed = Distance/Time

Downstream speed = u + v

Upstream speed = u - v

U and v are boat and stream speeds.

Calculation:-

We know,

66.67% = 2/3

(1 + 2/3) (8 - v) = 8 + v

40 - 5v = 24 + 3v

8v = 16

V = 2 km/hr

Required time = 60/(8 + 2) + 60/(8 - 2) = 16 hours.