There will also be a Exit Ticket on Schoology or Google Classroom
In my chemistry class, a percent (or a ratio) is always (part / whole) * 100%. The percent sign is a unit and has no numerical value. Also, as the unit canceling would show you, the percent must have the same units for the part and whole.
When someone is looking at Percent composition, it is a mass percent of the elements that make up the compound. As compounds are made up of the same ratio (arrangement) of elements, then the mass percent of each element in the compound is constant (i.e. Law of Definite proportion). This is one of the four parts of Dalton Atomic theory.