Problema Solution
A paddle boat can move at a speed of 18 km/h in still water. The boat is paddled 8 km downstream in a river in the same time it takes to go 4 km upstream. what is the speed of the river?
Answer provided by our tutors
let
x = the speed of the river
v = 18 km/h the speed of the paddle boat in still water
the speed upstream: v - x = 18 - x
the speed downstream: v + x = 18 + x
speed = distance/time => time = distance / speed
the boat is paddled 8 km downstream in a river in the same time it takes to go 4 km upstream
the time going 8 km downstream = the time going 4 km upstream
8/(v + x) = 4/(v - x)
8/(18 + x) = 4/(18 - x)
by solving we find:
x = 6 km/h
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the speed of the river is 6 km/h.