One easy way to model this problem is to keep track of the amount of salt and (salty) fluid in the tank separately. The fluid is simple: we have 200 liters initially, 6 liters are entering per minute and 8 are leaving, so the amount of fluids is 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 . For the salt we know this: per minute, we have 6 liters of a 5% solution flowing in, i.e. we have an inflow rate of salt of 0.3 liters. And we have 8 liters of fluid leaving, with a concentration equal to the amount of salt divided by the amount of fluid, i.e. with a salinity of 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 . Consequently, the differential equation that describes the amount of salt is given by
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LUkjbWlHNiMvSSttb2R1bGVuYW1lRzYiSSxUeXBlc2V0dGluZ0dJKF9zeXNsaWJHRic2JVE1b3V0cHV0fnJlZGlyZWN0ZWQuLi5GJy8lJ2l0YWxpY0dRJXRydWVGJy8lLG1hdGh2YXJpYW50R1EnaXRhbGljRic=
print( ); # input placeholder
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We know that at the beginning, the concentration is 20% and that there are 200 liters. So the initial amount of salt is 40 liters. We can solve the differential equation with these initial conditions:
QyQ+SSlzb2x1dGlvbkc2Ii1JJ2Rzb2x2ZUc2JCUqcHJvdGVjdGVkR0koX3N5c2xpYkdGJTYjPCRJLXNhbHRlcXVhdGlvbkdGJS8tSSJTR0YlNiMiIiEiI1MiIiI=
LUkjbWlHNiMvSSttb2R1bGVuYW1lRzYiSSxUeXBlc2V0dGluZ0dJKF9zeXNsaWJHRic2JVE1b3V0cHV0fnJlZGlyZWN0ZWQuLi5GJy8lJ2l0YWxpY0dRJXRydWVGJy8lLG1hdGh2YXJpYW50R1EnaXRhbGljRic=
print( ); # input placeholder
Ly1JIlNHNiI2I0kidEdGJSwoIiM1IiIiRicjISIiRikqJCwmISQrIkYqRidGKiIiJSMiIiQiKSsrKzU=
We could plot the amount of salt in tank, but the question asked for the salt concentration which is the ratio of salt amount and fluid volume:
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%;
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Of course, it makes no sense to evaluate the model beyond t=100 since that is when the water has all drained from it. On the other hand, up to then, the salt content drops steadily from the initial value (20%) to the salinity of the inflowing water that dilutes the water in the barrel. This is what we should have expected.