The best thing to do is to make sure that they're equal, and you should multiply 50 to get 400, rather than dividing 400 to get 50.
400/50= 8.
Therefore, you've got to multiply the 2% fat by 8, 1x8= 8, 50x8=400.
Therefore, the 2% fat has 8 parts milk,
Meaning that the whole milk has more days per part.
Hope this helps :)
