What is the combined velocity of a boat traveling 20 km/hr East on a river that is flowing 15 km/hr West?

5 km/hr East

Explanation:

The resultant velocity when two objects go in opposite direction is given by the sum of the velocities. Given that the river current flows West at 15 km/h but the boat goes East at 20 km/hr, we take East as positive and West as negative. The resultant velocity will be

20-15=5 km/hr

Since velocity must have direction component, and we have final answer as positive, then the direction is East