To complete this calculation in excel you need to use a simple formula in a cell as below:
=YourNumber*(1-0.2)
Examples of How To Take 20% in Excel
Using a number eg 20:
=20*(1-0.2)
Using a cell eg a1:
=A1*.8
If the percentage to be deducted is found in another cell (say B1), then you can format that cell as % and use this sort of formula.
=A1*(1-B1)
More Advanced Techniques for 20% Calculations
=Round(A1*.8,0)
If the percentage to be deducted is found in another cell (say B1), then you can format that cell as % and use this sort of formula.