Posted by lisa on .
A dehydrated patient needs a 7.9% saline IV. Unfortunately, the hospital only has bags of 3% and 10% saline solutions. How many liters of each of these solutions should be mixed together to yield 3 liters of the desired concentration?

algebra 
helper,
x = liters of 3% solution
3  x = liters of 10% solution
.03x = value 3% solution
.10(3  x) = value 10% solution
3 = liters of 7.9% mixture
.079(3) = 0.237 = value 7.9% mixture
.03x + .10(3  x) = 0.237
Solve for x, which is number of liters of 3% solution.
(3  x) = number of liters of 10% solution