how to calculate equity that isnt 50/50?

[b33nz]

ive been wondering what formula do i use to calculate equity that doesnt happen equally.

what i mean by '50/50' is lets say you are gonna win $100 50% and lose $50 50%. so then its easy you just take 100 - 50 = +$50 on average.

but now lets say you are gonna win $100 75% and lose $50 25%. what formula would i need to calculate the correct amount?