A dairy needs 291 gallons of milk containing 6% butterfat. How many gallons each of milk containing 7% butterfat and milk containing 4% butterfat must be used to obtain the desired 291 gallons?

Step-by-step explanation:

Each gallon of 7% milk contains 0.07 gallon of butterfat.

Each gallon of 4% milk contains 0.04 gallon of butterfat.

291 gallons of 6% milk contain 291×0.06 = 17.46 gallons of butterfat.

Let x be the number of gallons of 7% milk used. 291-x is the number of gallons of 4% milk used.

0.07x + 0.04(291-x) = 17.46

0.03x + 11.64 = 17.46

x = 200

Use 200 gallons of 7% and 91 gallons of 4%.

option 1

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