A boat which travels at 2.5 km per hour relative to the water aims straight for the opposite bank of a 84.4 m wide river. If it reaches the opposite side 253.2 m downstream, what is the speed of the river?

The speed of the river adds to, or subtracts from, the speed of the boat. You should be able to solve the problem with that information.

Split the problem into two components -- a cross-stream component and a downstream component. Solve the problem that way.

7.5 km/hr

2.5 km/hr = 41.66 m/m relative to the river (frame of ref)

to travel 84.4 m at that speed takes 2.0256 min

in 2.0256 min the river has traveled 253.2 m

125 m/min = 7500 m/h = 7.5 km/h


malcolm