math

donna took 3hours to row 18 km upstream. her return trip took 1 hour less. find the rate of rowing in still water and the rate of the current.

let the speed of her rowing in still water be x km/h, let the speed of the current be y km/h
going with the current: speed is (x+y), time = 2 hours
going against the current: speed is x-y, time is 3 hours

so:
2(x+y) = 18 ----> x+y=9
3(x-y) = 18 ----> x-y=6

adding these two gives 2x=15
x=7.5, backsubstitute for y=1.5



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