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Homework Help: Mixing problems

  1. Feb 5, 2006 #1
    A tank contains 1920 L of pure water. A solution that contains .07 kg of sugar per liter enters tank at the rate 7 L/min. The solution is mixed and drains from the tank at the same rate. With S representing the amount of sugar (in kg) at time t (in minutes) write a differential equation which models this situation.

    S'(t)=r1c1-r2c2
    r1=r2=7
    c1=.07kg
    c2=S(t)/V(t)=S/1920

    so wouldnt [tex]S'(t)=.049- \frac{7S}{1920}[/tex]

    I'm not sure why this is wrong
     
  2. jcsd
  3. Feb 5, 2006 #2

    HallsofIvy

    User Avatar
    Science Advisor

    Would you believe arithmetic? 0.07*7= 0.49, not 0.049!!
     
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