To find a relative percentage decrease via a growth factor, you need to find the decay rate, by using the formula 

A decay factor helps you calculate a final amount after a percentage has been subtracted. It is given by the formula:

 is the decimal representation of the percentage that is being subtracted.

Indicates the percentage decrease between the initial and final amounts. Also known as decay rate.

The starting amount, before a percentage increase or decrease

The amount after you have included the percentage increase or decrease. It is given by the formula:

A measure of how much a quantity has changed expressed as percentage (%)

Mathagon

Growth Factor

Growth Factor for an Increase

Decay Factor

Decay Factor for a Decrease

Growth Factor Equal to 1

Finding the Initial Amount 

Finding a Percentage Increase

Finding a Percentage Decrease

Increasing by the Same Percentage Multiple Times

Decreasing by the Same Percentage Multiple Times

Growth Factors

To find the relative percentage change via growth factor, you need to find the growth or decay rate, by using the formula y =a (1 ± r). This video explains. 

How Do You Find a Percentage Decrease Using a Decay Factor?