A boat travels downstream at 15.5 km/h and upstream at 8.5 km/h. What is the velocity of the current?

Explanation

The speed of the current is calculated by taking half the difference between the downstream and upstream speeds. Given the downstream speed is 15.5 km/h and the upstream speed is 8.5 km/h, the speed of the current = (15.5 - 8.5) / 2 = 3.5 km/h.