Countercurrent speed = ship speed-current speed

Downstream speed-countercurrent speed =2 water flow speed

When a ship sails between two docks, it takes 6 hours to sail downstream and 8 hours to sail upstream. The speed of water is 2.5 kilometers per hour. Find the speed of the ship in still water.

Assume that the still water velocity is x.

Using the formula of running water problem, paddle speed+current speed = downstream speed-current speed = countercurrent speed.

6(X+2.5)=8(X-2.5)

6X+ 15=8X-20

2X=35

X= 17.5

The speed of the ship in still water is17.5 km/h.