To decrease a number by a percent, what must you do?

To decrease a number by a percent, it is essential to subtract the calculated percent of that number from the original value. When you are given a percentage, you first convert that percentage into a decimal and then multiply it by the original number to find out how much to decrease.

For example, if you need to decrease a number by 20%, you would first convert 20% into decimal form, which is 0.20. Then, if the original number is 100, you would calculate 0.20 multiplied by 100, giving you 20. Finally, you would subtract this 20 from the original number (100), resulting in 80.

This process illustrates how subtraction is utilized in finding the new value after a percentage decrease. Therefore, the correct approach to decrease a number by a percent is to subtract that calculated amount from the original.