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ODE mixture question

  • Thread starter cue928
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  • #1
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Tank w/ 100 gal pure water. At time = 0, sugar/water mixture with .2 lbs of sugar per gallon enters at 3 gal/ minute. Drain opened at bottom allows sugar solution to leave at 3 gal per minute. Perfect (lol) mixing occurs.

I show the following:
Rate in: .2 x 3 = .6
Rate out: x/100
Volume: 100

dA/dt = .6 - A/100; I get an integrating factor of e^x/100. It asks what will the sugar content be after 20 minutes. I came up with a C value of 19.4. I get 16.##, they get 9.0348. Any idea where I'm going wrong?
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
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hi cue928! :smile:
Tank w/ 100 gal pure water. At time = 0, sugar/water mixture with .2 lbs of sugar per gallon enters at 3 gal/ minute. Drain opened at bottom allows sugar solution to leave at 3 gal per minute. Perfect (lol) mixing occurs.

dA/dt = .6 - A/100
oooh :cry: … what happened to the (second) 3 gal per minute? :redface:
 

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