SOLUTION: Juniors boat will go 15 miles per hour in still water. If he can go 12 miles downstream in the same amount of time as it takes to go 9 miles upstream, then what is the speed of th

Question 304186: Juniors boat will go 15 miles per hour in still water. If he can go 12 miles downstream in the same amount of time as it takes to go 9 miles upstream, then what is the speed of the current.
Word problems are definitely my weakness, they just don't make sense in my head. I have a hard time figuring out which formula I need and what I need to do.
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
Juniors boat will go 15 miles per hour in still water.
If he can go 12 miles downstream in the same amount of time as it takes to go 9 miles upstream, then what is the speed of the current.
;
See if this makes sense to you.
:
Let c = speed of the current
then
(15+c) = speed down stream
and
(15-c) = speed upstream
:
Write a time equation: Time = dist/speed
Time up = time down
=
cross multiply
9(15+c) = 12(15-c)
:
135 + 9c = 180 - 12c
:
9c + 12c = 180 - 135
:
21c = 45
c =
c = 2.143 mph is the current
;
:
Check solution, by finding the times (they should be equal)
9/12.857 = .7 hrs (subtracted the speed of the current from 15)
12/17.143= .7 hrs (added the speed of the current to 15)
:
How about this, did I explain this so you can see it?

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