SOLUTION: I know there's a similar problem, but got very confused by the way the set-up was formatted in the response. Can someone pllleeeeease help? All I need is to see which numbers & v

Question 23019: I know there's a similar problem, but got very confused by the way the set-up was formatted in the response. Can someone pllleeeeease help? All I need is to see which numbers & variables go where, then I should be able to solve it. Thanks in advance!
In still water a boat can travel 15 mph. It travels 36 miles upstream & 36 miles downstream in a total time of 5 hours. Find the speed of the current. (The book says the answer is 3 mph)
Found 2 solutions by rapaljer, stanbon!:
Answer by rapaljer(4671) (Show Source): You can put this solution on YOUR website!
Let x = speed of the current
15 +x = speed of the boat downstream (with the current)
15-x = speed of the boat upstream (against the current)
Distance upstream = Distance downstream = 36 miles

D=RT
T= D/R

Total Time = D/R + D/R = 5 hours

Multiply both sides of the equation by the LCD which is (15+x)(15-x):

x= 3 or x= -3

Reject the negative answer. x=3 mph = speed of the current.

R^2 at SCC

Answer by stanbon!(97) (Show Source): You can put this solution on YOUR website!
Use d=rt in he form t=d/r
Let the current speed be represented by "c".
Upstream Data:
d=36; rate= 15-c; therefore time upstream = 36/(15-c)
Downstream Data:
d=36; rate = 15+c; therefore time downstream = 36/(15+c)
EQUATION:
Time up + Time down = 5 hrs
36/(15-c) + 36/(15+c) = 5
1/(15-c) + 1/(15+c) = 5/36
30/(225-c^2) = 5/36
6/(225-c^2) = 1/36
6(36) = 225-c^2
-c^2 = -9
c = 3 mph (speed of current)
Cheers,
Stan H.
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