Original: 150 T-shirts

New: 120 T-SHIRTS

Since the new amount is greater than the original, this is a percent of increase.

The amount of change = new T-shirts – original T-shirts.

The amount of change = . \ \

Let r be the percentage of increase.

Use the original number, 150 as the base.

The percent proportion is

\ \

To solve for r, first find the cross products.

                                  (Multiply: )

                            (Divide each side by 150)

                                        (Cancel common terms)

                                                (Divide: )

The percentage of increase by 20%

The percent of change is a percent of increase.

The percentage of increase by 20%.