SOLUTION: A dehydrated patient needs a 6.8% saline IV. Unfortunately, the hospital only has bags of 4% and 7% saline solutions. How many liters of each of these solutions should be mixed tog

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: A dehydrated patient needs a 6.8% saline IV. Unfortunately, the hospital only has bags of 4% and 7% saline solutions. How many liters of each of these solutions should be mixed tog      Log On


   

Question 500158: A dehydrated patient needs a 6.8% saline IV. Unfortunately, the hospital only has bags of 4% and 7% saline solutions. How many liters of each of these solutions should be mixed together to yield 3 liters of the desired concentration?
x=4% saline solutions
y=7% saline solutions
x+y=3
.04x+.07y=.068
x=3-y
.04(3-y)+.07y=.068
.12-.04y+.07y=.068
.03y=-.052
y=-1.73
x+-1.73=3
x=4.73
4.73+-1.73=3
3=3
.04(4.73)+.07(-1.73)=.068
.189-.121=.068
.068=.068
Answer by mananth(16949) About Me  (Show Source):
You can put this solution on YOUR website!
percent percent ---------------- quantity
Saline I 4 ---------------- x liters
Saline II 7 ---------------- 3 - x liters
Mixture 6.80% ---------------- 3

4x+7(3-x)=6.8* 3

4x+21-7x=20.4
4x-7x= 20.4 - 21
-3x= -0.6
/ -3
x=0.2 liters 4.00% Saline I
2.8 liters 7.00% Saline II