SOLUTION: A moterboat can go 8 miles downstream in 20 mins. It takes 30 mins for this boat to go back upstream the same 8 miles. Find the speed of the current.

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Question 27194: A moterboat can go 8 miles downstream in 20 mins. It takes 30 mins for this boat to go back upstream the same 8 miles. Find the speed of the current. I know how to set everything up except for the rate. PLEASE HELP!!!!

Thank You,
Stacy
Answer by Paul(988) About Me  (Show Source):
You can put this solution on YOUR website!
20 minutes = 1/3 hours.
30 minutes = 1/2 hours.
Let the speed of the boat be y.
Let the speed of the current be x.


8%2F%28x-y%29%2F3=8%2F%28x%2By%29%2F2
%28x%2By%29%2F2=8 ---> solve for y
x-y=16
y=16+x (subsitution)

(x+y)/2=8
x+y=24 (subsitue for y)
x+(16+x)=24
x+16+x=24
2x=8
x=4
y=16+4
y=20

Hence, the speed of the boat is 20mph and the speed of the current is 4mph.