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Help with free PREP flash card question

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Help with free PREP flash card question

by lorivogue » Mon Jan 26, 2009 6:18 am
Can someone explain this flash card mixture question:

How many liters of a solution that is 15% salt must be added to 5 liters of a solution that is 8% salt so that the result mixture is 10% salt?

.15n + .08(5) = .1(n+5)
15n + 40 = 10n +50
5n = 10
n = 2 liters

My confusion llies in the ".1(n+5).
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by DanaJ » Mon Jan 26, 2009 6:35 am
The first line is about the respective quantities of salt in all three solutions of salt.
The first solution is 15% concentrated, but we do no know how much solution in liters we have. Therefore, the amount of salt in this particular solution is 15%*n = 0.15n
The second solution is 5liters in volume and 8% salt, meaning it has a salt content of 8%*5 = 0.08*5
The third solution is actually the previous two put together. Its volume will be n + 5. Its concentration is set at 10%, so the salt content will be 10%*(n+5) = 0.1*(n+5).

Hope this helps.
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