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

Respuesta :

CastleRook
let them rate of the stream be x:
speed of boat and river upstream is:
(9-x) mi/hr
speed of boat and river down stream is:
(9+x) mi/hr
time taken to move upstream is:
time=distance/speed
=(9-x)/10

time taken to move downstream is
time=(9+x)/20
since they took the same time, we shall have:
(9-x)/10=(9+x)/20
solving for x we get:
20(9-x)=10(9+x)
180-20x=90+10x
180-90=10x+20x
90=30x
hence
x=3 mi/hr
thus the speed of river current is 3 mi/hr

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