If you have 8 cups of milk at 1% butter fat and want to add milk that is 4% butter fat so the whole mixture is 2% butter fat how many cups would you need to add?

8(0.01)+0.04x=0.02(x+8) 

m100: 
8(0.01)+0.04x=0.02(x+8) 


8+4x=2(x+8) 


8+4x=2x+16 

4x-2x=16-8 


2x=8 


x=4 

Add 4 cups 

:)