Describes how much oa quantity decrease in comparison to the original quantity

Your question is a little bit unclear but I'll try to help:

When quantity increases, we can calculate it's percent increase using equation.
PERCENT INCREASE= (new amount−original amount)/original amount}

You can also multiply it by 100% go tet percent value.

When quantity decreases, you can calculate it's percent increase using equation.
PERCENT DECREASE=(original amount−new amount)/original amount

You can also multiply it by 100% go tet percent value.