The document discusses percentage calculations and percentage change. It provides examples of calculating percentages of totals and calculating percentage increases or decreases. Specifically, it shows how to calculate what percentage one number is of another total using the percentage formula. It also demonstrates calculating percentage change by taking the increase or decrease amount and dividing it by the original value before the change. Sample problems are worked through, such as calculating the percentage temperature increase from 16 to 29 degrees Celsius and calculating the percentage weight decrease of a rock if half the water it absorbed is removed.