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Working with percents.
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What is 55% of 400?
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Or 240 is 30% of what number?
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Now these could be test problems in and of themselves.
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They certainly would be things you might have to do in the context of
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a larger problem.
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So in this video I will show a few ways to tackle questions such as this.
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The first really big idea is Percents as Multipliers.
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The decimal form of percent is called the multiplier for that percent.
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This is because we can simply multiply by this form to take a percent of the number.
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So when we're using percents as multipliers,
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here are the basic things to remember.
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Remember that is means equal.
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Remember that of means multiply.
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Change any percent to the multiplier form and replace unknowns with a variable.
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So, for example, what is 80% of 200?
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The what, the unknown, that will be x.
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Is, that becomes equal.
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80%, that will become the multiplier, .8.
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And then we'll multiply that of, times 200.
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So translating that sentence into math,
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we get (.08) x (200), we multiply out, we get 160.
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Similarly, 240 is 30% of what number?
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240 equals, 30%, is 0.30,
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times and then what number, x.
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So translating to math.
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Then, of course, we divide.
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Move the decimal place over and divide out, we get 800.
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Now the second way to use this is in questions
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where we have to find the percent.
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So 56 is what percent of 800?
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So here we set things up again.
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56 equals x times 800 and
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we'll have to remember that that x of course is a multiplier.
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So we divide out, we can cancel the factor of 8, we get 7 over a 100, which is 0.07.
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That's a multiplier which corresponds to 7%.
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Finally, percents and fractions.
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Use this approach only if the percent is a very easy fraction.
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For example, one half or one quarter.
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So, if it's a very easy fraction,
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then sometimes it's easier to change things to a fraction.
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So, we get the question, what is 75% of 280?
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Well, it's much easier just to remember, 75%, that's three quarters.
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What's three quarters of 280?
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Cancel the 4s, we get 3 times 70, which is 210.
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Here are some practice problems, so pause the video and practice these now.
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Here are the answers.
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So in summary, use percents as multipliers,
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that is their decimal form, and the method for solving the simple percent problems.
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Using the same method to find an unknown percentage.
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So, there the unknown would be the percentage of itself.
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We'll get a decimal value.
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We'll have to remember that as the multiplier form,
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the decimal form of a percent.
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And then we can use certain fraction shortcuts for percents.