• The answer here is 17.2. Solving this problem is very simple. There are three situations all involving the same method Situation 1: What IS 21% of 82? Situation 2: 17.2 is 21% OF what? Situation 3: 17.2 is what percentage of 82? So in all the situations, there are 3 things to work with: The OF number The IS number and a Percentage. One of these will be what you're looking for. Call this X. As previously stated, It can be either the percentage, the IS number, or the OF number. Here's how to do it: Set up 2 fractions, like in a ratio. If you have the percentage, put that number over 100. 21 --- 100 Then, for the second fraction, put the OF number on the bottom, and the IS number on the top. In your problem we have the number 82: "What IS 21% OF 82?" Therefore, 82 goes on the bottom. We don't have the IS number, so that is X. X --- 82 Now, you have 21 X --- . --- 100 82 Cross multiply and then divide: 82 X 21 =1722 Now divide 1722 by 100 1722/100 = 17.2 17.2 is your answer. This works for all problems like this. "IS OVER OF".
• 8-18-2017 There is a process called "estimating". It is taught as a junior level course in engineering majors. It deals with problems very much more complex than what you have presented. What you want is arithmetic, and we do not estimate in arithmetic; we calculate. 21% means 21/100 which means 21 marks on a ruler with 100 marks. So if 100 marks are worth 82 then each mark is worth 0.82 and 21 marks are worth 21 x 0.82 = 17.22 EXACTLY!