In whole milk, 13 parts out of 400 are milk fat. in 2% milk, 1 part out of 50 is milk fat. which type of milk has more milk fat per cup?

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 :)

A= b/2 because u simplying both sides of equation

I’m having a hard time understanding your question