Question 287930
Let x be number of gallons at 16%
let 40-x be number of gallons at 48%
You want to end up with 40 gallons at 30%

Sooo, off to the races!
x(.16) + (40-x)(.48)=40(.30)
(let's multiply by 100 to remove the decimal)
16x+48(40-x)=(40)30
16x+1920-48x=1200 (do the math)
16x+1920-48x=1200
-32x=-720
x=-720/-32
x=22.5                (I said 720/32=27.5---I caught my simple dividing mistake because I always double 
                                 check.)
Sooo 22.5 gallons of 16% butterfat and
          17.5 gallons of 48% butterfat must be mixed to yield 40 gallons of 30% butterfat! I have to run.       Always check your work. Plug in the numbers and see if they work!!!! Later...(I divided wrong at first--I said 4-4=1 (DUuu)---This threw the whole answer off! I caught my mistake because I  re-checked AND double checked. Be careful in the simple arithmetic. WE ALL MAKE MISTAKES!!!!!!!