Rates

In mathematics, a rate is the ratio between two related quantities in different units. If the denominator of the ratio is expressed as a single unit of one of these quantities, and if it is assumed that this quantity can be changed systematically (i.e., is an independent variable), then the numerator of the ratio expresses the corresponding rate of change in the other (dependent) variable

Or simply a ratio between two related quantities in different units.

Also make sure to pay attention to the information given and the information that is being asked for in the question.

Oftentimes a question will have an abundance of information and the question will ask about a summative or small part of the total information.

This would include receipts amongst many examples