Original: 50

New: 70

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

The amount of change = New Amount – Original Amount.

 The amount of change = .

Let r be the percentage of increase.

Use the original number, 50 as the base.

The percent proportion is

To solve for r, first find the cross products.

                                  (Multiply: )

                            (Divide each side by 50)

                                      (Cancel common terms)

                                              (Divide: )

The percentage of increase by 40%

The percent of change is a percent of increase.

The percentage of increase by 40%.