SOLUTION: Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her bo

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Question 60115This question is from textbook Elementry and Intermediate Algebra
: Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water? This question is from textbook Elementry and Intermediate Algebra

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water?
:
Since we are dealing in mph, change 20 min to hrs: 20/60 = 1/3 hr
:
Let s = her speed in still water
Then (s+4) = her speed down-stream
And (s-4) = her speed up-stream
:
Time = dist/speed
:
Time to go upstream - (1/3) hr = time to go down stream
5%2F%28s-4%29+-+1%2F3+=+5%2F%28s%2B4%29
:
Mult equation with the common denominator; 3(x-4)(s+4), resulting in:
3(s+4)(5) - 1(s+4)(s-4) = 3(s-4)(5)
:
3(5s + 20) - 1(s^2 - 16) = 3(5s - 20)
:
15s + 60 - s^2 + 16 = 15s - 60
:
-s^2 + 15s - 15s = -60 - 60 - 16
:
-s^2 = - 136
:
s^2 = 136
:
s = SqRt(136)
:
s = 11.66 mph in still water
:
:
Check using time equation:
5/7.66 - .33 = 1/15.66
.65 - .33 = .32