SOLUTION: One boat travelling 15 mph goes 36 miles downstream in the same amount of time that another boat going 20 mph goes 34 miles upstream. How fast is the current in mph?

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Question 680484: One boat travelling 15 mph goes 36 miles downstream in the same amount of time that another boat going 20 mph goes 34 miles upstream. How fast is the current in mph?

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
One boat traveling 15 mph goes 36 miles downstream in the same amount of time that another boat going 20 mph goes 34 miles upstream.
How fast is the current in mph?
:
Let c = the speed of the current
then
(15+c) = effective speed downstream
and
(20-c) = effective speed upstream
:
Write a time equation; time = dist/speed
:
36%2F%28%2815%2Bc%29%29 = 34%2F%28%2820-c%29%29
cross multiply
34(15+c) = 36(20-c)
510 + 34c = 720 - 36c
34c + 36c = 720 - 510
70c = 210
c = 210/70
c = 3 mph is the current
:
:
Confirm this by seeing if their times are equal.
36/18 = 2hr downstream
34/17 = 2hr upstream