Question

A boat moves downstream at the rate of 1 km in 3(1/3) minutes and upstream at the rate of 10km an hour. What is the speed of the boat in still water(in km/hr)?

1. 10
2. 12
3. 14
4. 16
5. 18

Answer 1

Correct Answer - Option 3 : 14

Given:-

Time for 1 km downstream distance = 3(1/3) minutes

Time for 10 km upstream = 1 hour.

Formula:-

Speed = Distance/Time

Downstream speed, D = u + v

Upstream speed, U = u – v

Speed of boat in still water = ½ (U + D)

u and v are boat and stream speeds.

Calculation:-

Time in hour = 3(1/3)/60 = 1/18

Downstream speed = 1/(1/18) = 18 km/hr

Upstream speed = 10 km/hr

Speed of boat in still water = ½ (18 + 10) = 14 km/hr