SOLUTION: Jessica can row 3 miles uptstream in the same time it takes to row 5 miles downstream. If the speed of the current is 10mph, what is the speed of the rowboat in still water?

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Question 518847: Jessica can row 3 miles uptstream in the same time it takes to row 5 miles downstream. If the speed of the current is 10mph, what is the speed of the rowboat in still water?
Found 2 solutions by richwmiller, Maths68:
Answer by richwmiller(17219) (Show Source):
You can put this solution on YOUR website!
(r-10)*t=3
(r+10)*t=5
rt-10t=3
rt+10t=5
2rt=8
rt=4
4-10t=3
1=10t
1/10=t
r/10=4
r=40
That's crazy!
Nobody rows 40 mph

Answer by Maths68(1474) (Show Source):
You can put this solution on YOUR website!
Speed of boat = b
Speed of current = c = 10mph
Time = t
Distance = Speed * time
time = Distance/Speed

Jessica can row 3 miles uptstream
Time=distance traveled/(Speed of boat - Speed of Current)
t=3/(b-10)��(1)
It takes to row 5 miles downstream.
Time=distance traveled/(Speed of boat + Speed of Current)
t=5/(b+10)��(2)

Since time taken in both cases is same therefore
3/(b-10)=5/(b+10)
3(b+10)=5(b-10)
3b+30=5b-50
3b-5b=-30-50
-2b=-80
-2b/-2=-80/-2
b=40
The speed of the boat in still water = 40 mph
Check
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Against the current
Speed = boat - current
Speed = 40-10
Speed =30
Time taken to travel 3 miles upstream
t=3/(b-10)
t=3/(40-10)
t=3/30
t=1/10 = 6 minutes
With the current
Speed = boat + current
Speed = 40+10
Speed =50
Time taken to travel 5 miles downstream
t=3/(b+10)
t=3/(40+10)
t=5/50
t=1/10 = 6 minutes
Is it possible to row that fast!!!!!!!