25% of Water to Oil. In this case if you have 100g of oil you would use 25g of water.
Here is how it works: Cross Multiplication
25%/100% = Xg/100g
No multiply 25x100 = 2500
Now multiple 100 times X = 100X
So 2500 = 100X
Divide both sides by 100 and you get 25 = X
Hope...