Percentages are calculated by using the following equation:
amount/total = percentage
Note: Percentage is in decimal format.
For demonstration I have get percentage of get marks as below image data.
Now, let's say that you want to reduce a particular amount by %, like when you're trying to apply a discount. Here's a formula that would get you that result. (Think of the 1 in the formula below as a stand-in for 100%.)