Whether you need to solve a mathematical equation or use it for a practical purpose, finding the percentages of a number can be difficult without knowing a few basic concepts in math. From calculating how much tip to leave on a restaurant bill to figuring out how much you save on an item, calculating the top 20 percent can be helpful in your daily life as well as in the classroom.

You can compare your class rank with the answer you found in Step 3. If your ranking is higher, which means the number is smaller, you are part of the top 20 percent of your class.

Convert 20 percent into a decimal by dividing it by 100. If you do not have a calculator, you can simply move the decimal places two spaces to the right of the number to get 0.20 ( 20/100 = 0.20).

Find the number you are trying to calculate the top 20 percent for. For example, if you are calculating the top 20 percent of a high school class, the number would be the total number of students in the class. For a clothing sale, the number would the price of the clothes.

Take the number you found in Step 2 and multiply it by 0.2. For example, If a pair of jeans cost $50 and there is a 20 percent sale on everything in the store, you would save $10 ( 50 x 0.2 = 10).