Explain why a change from 20 to 40 is a 100% increase, but a change from 40 to 20 is a 50% decrease.





Increasing 20 to 40 is the same as increasing 20 by c. So, it is a 100% increase. Decreasing 40 to 20 is the same as decreasing 40 by one-half of c. So, it is a 50% decrease.
I don't understand how to fill in the blanks.