Question 305750
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Let *[tex \Large x] represent the number of gallons of cream required.  Then *[tex \Large 90\ -\ x] represents the amount of 2% milk you need to add to get a total of 90 gallons.


There are *[tex \Large 0.22x] gallons of pure butterfat in the cream and *[tex \Large 0.02(90\ -\ x)] gallons of pure butterfat in the 2% milk, and once you have 90 gallons of 4% milk you will have 90 times 0.04 = 3.6 gallons of pure butterfat.


So:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ 0.22x\ +\ 0.02(90\ -\ x)\ =\ 3.6]


Just solve for *[tex \Large x]


John
*[tex \LARGE e^{i\pi} + 1 = 0]
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