if creamery is 22% butterfat. how many gallons of cream must be mixed with milk testing at 2% butterfat to get 20 gallons of milk containing 4% butterfat

Answer 1

.22 c + .02 m = .04(20)
c + m = 20 so m = (20-c)
so
.22 c +.02(20-c) = .8

Answer 2

add up the amount of fat in the milk and cream. It must equal the amount in the mix. If there are x gallons of cream, then the rest (20-x) is milk. So,

.22x + .02(20-x) = .04(20)

Answer 3

An ice cream maker decided that ice cream with the 9% butterfat is the best to sell. How many gallons of ice cream with the 5% butterfat should be mixed with ice cream that is 15% butterfat to make 100 gallons of the desired blend