A group rate describes successes, defects or ingredient mass relative to that group's own base. To combine groups, return to the underlying amounts. This lesson builds that method, shows when averaging rates is justified, and connects a table, a pie chart and count bars without silently changing the denominator. You should be comfortable finding a percentage of a whole and distinguishing a percentage-point difference from relative percentage change. Throughout the examples, the given counts and percentages are exact unless a question says otherwise.