Calculating the percentage of two numbers tells you how much they've changed.
Calculating a percentage isn't limited to figuring out how much that sale percentage will save you at the store. Percentages also tell you how much something has changed and what proportion you're dealing with. The process you have to go through to calculate them isn't that different, though, and still relies on multiplying and dividing one of the two numbers into the other.
Instructions
1. Divide the smaller number by the bigger number if you want to find out what percentage the smaller number is of the bigger number. For example, if you eat six doughnuts out of 10, divide 6 by 10 to find that you've eaten 60 percent of the doughnuts.
2. Multiply the larger number by 100 and divide that product by the smaller number to get the percentage form of how much extra work you've done, food you've made or other activity that's exceeded original expectations. For example, if you have a quota to meet when delivering fliers of 200, and you deliver 250, set up a ratio with 200 fliers over 100 percent and 250 fliers over X percent. Cross-multiply like you would when solving for X in a ratio -- 250 x 100 = 25,000, and 200 * X = 200X -- and divide 25,000 by 200 to get 125 percent. Alternately, you can divide the bigger number by the smaller and multiply the result by 100.
3. Calculate the percentage difference of a change in numbers by dividing the difference between the two by the number before the change and multiplying by 100. So if you have 15 milliliters of water in a beaker one week, and the next week you find some of it has evaporated and you have only 12 milliliters, subtract 12 from 15 to get 3, and divide 3 by 15 to get 0.2. Multiply that by 100 to find that 20 percent of the water has evaporated.
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