algebra
posted by sh .
Nurse erika needs to prepare 12 liters of a 10% saline solution. The stockroom only has 7 % and 15% saline solutions. How much of each solution should erika mix together to get 12 litres of a 10% saline solution

let amount of 7% solution be x L
then the amount of 15% solution must be 12x L
.07x + .15(12x) = .10(12)
times 100
7x + 15(12x) = 120
7x + 180  15x = 120
8x = 60
x = 7.5
She should use 7.5 L of the 7% and 4.5 of the 15% solution
check:
.07(7.5) + .15(4.5)
= 1.2
and 10% of 12 L is 1.2