Question

Brian's boat has a top speed of 9 miles per hour in still water. While traveling on a river at top speed, he went 10 miles upstream in the same amount of time he went 20 miles downstream. Find the rate of the river current.

Answer 1

let the speed of the river current be x mph
speed going upstream = 9 -x mph
speed going downstream = 9 + x mph

10/(9-x) = 20/(9+x)
90 + 10x = 180 - 20x
30x = 90
x = 3

the speed of the river is 3 mph