SOLUTION: A dehydrated patient needs a 8.15% saline IV. Unfortunately the hospital only has bags of 8% and 10% saline solutions. How many liters of each of these solutions should be mixed

Question 479291: A dehydrated patient needs a 8.15% saline IV. Unfortunately the hospital only has bags of 8% and 10% saline solutions. How many liters of each of these solutions should be mixed together to yield 4 liters of the desires concentration?
I don't know where to start.
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
A dehydrated patient needs a 8.15% saline IV. Unfortunately the hospital only has bags of 8% and 10% saline solutions. How many liters of each of these solutions should be mixed together to yield 4 liters of the desires concentration?
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Equation:
salt + salt = salt
0.08x + 0.10(4-x) = 0.0815*4
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0.08x + 0.40 - 0.10x = 0.0815*4
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Multiply thru by 10000 to get:
800x + 4000 - 1000x = 815*4
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-200x = -740
x = 3.7 liters (amt. of 8% solution needed)
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4-x = 4 - 3.7 = 0.3 liters (amt. of 10% solution needed)
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Cheers,
Stan H.
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