Adding a function or logic to a formula

Hello,

I have set up a few simple formulas on a spreadsheet to calculate different distribution of figures for based on total purchase. For example, if the total purchase amount is $50,000, then 25% of that is based on this type of sale, 50% is based on another type and the remaining 25% is based on the last type. The simple formulas are working correctly to get the right numbers based on the total amount.

is there a way I can add logic or function to this so if my users changed the % of distribution, the formula for that distribution % can automatically be updated to calculate correctly rather than having to update the formula manually?