List the mathematical formula according to the meaning of the question: 20 divided by 80 and then multiplied by 100%.

The calculation method is as follows: according to the arithmetic rule of mathematical multiplication and division, divide the first two terms, and then multiply the quotient with the latter to get the result. That is: 20 divided by 80 and then multiplied by 100%, 20 divided by 80 equals 0.25, and then multiplied by 100%, and the final result equals 25%.