How many grams of cream with 10% fat should a barista add to 120 grams of 20 % fat to get a mixture with 18 % fat
.10x + .20(120) = .18 ( x + 120) simplify
.10x + 24 = .18x + 21.6
24 - 21.6 = .18 x - .10x
2.4 = .08x
2.4 / . 08 = x = 30 grams
