SOLUTION: Stee Deitmer takes 1.5 times as long to go 72 miles upstream in his boat as he does to return. If the boat cruises at 30 mph in still water, what is the speed of the current?

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Question 437099: Stee Deitmer takes 1.5 times as long to go 72 miles upstream in his boat as he does to return. If the boat cruises at 30 mph in still water, what is the speed of the current?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
Deitmer takes 1.5 times as long to go 72 miles upstream in his boat as he does to return.
If the boat cruises at 30 mph in still water, what is the speed of the current?
:
Let c = speed of the current:
then
(30+c) = effective speed downstream
and
(30-c) = effective speed upstream
:
Write a time equation, time = dist/speed
:
Time upstream = 1.5 times time downstream
72%2F%28%2830-c%29%29 = 1.5(72%2F%28%2830%2Bc%29%29)
which is
72%2F%28%2830-c%29%29 = 108%2F%28%2830%2Bc%29%29
Cross multiply
72(30+c) = 108(30-c)
2160 + 72c = 3240 - 108c
72c + 108c = 3240 - 2160
180c = 1080
c = 1080%2F180
c = 6 mph is the rate of the current
:
:
Check this by finding the actual times
72/36 = 2hr
72/24 = 3hrs, which is 1.5 times 2 hrs