Three quick percentage modes
Use % of a number when you have a percentage and a value. Use X is what % of Y when you want to express one number as a percentage of another (great for marks, market share, or discounts). Use % increase / decrease when you have an old and new value and want to know the percentage change.
Want the deeper explainer?
Read Percentage rules: every formula you actually need for worked SA examples and the reverse-VAT trick.