Question

Steve can kayak at 8 km/h in still water. On the river, Steve and the kayak travel slower upstream due to the current. It takes him 1.5 h for a trip downstream, but
3.25 h for the same distance upstream. Determine the speed of the river’s current.

Answer 1

Let distance be D km, and
the current be C km/h
His speed is 8 km/h in still water.
So his speed upstream is
D/3.25=8-C
and downstream,
D/1.5=8+C

Cross multiply each to get
D = 3.25(8-C)
D=1.5(8+C)

Solve by comparison
1.5(8+C)=3.25(8-C)
Isolate C
4.75C = 8(3.25-1.5)
C=8*1.75/4.75
= 2.9 km/hr approximately

Check that the solution works by substituting the solution into the original equations.