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Hey it’s Professor Dave; let’s work with
percentages.
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We are all aware of percentages, as they are
ubiquitous in society.
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There is a sale today, thirty percent off.
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Leave a twenty percent tip after the meal.
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Today there is a fifty percent chance of rain.
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So what are these things?
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Well in Latin, centum means one hundred, so
percent literally means out of a hundred.
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It’s just a way of conveying magnitude,
by modifying some total into a hundred, and
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then reporting a value of interest as some
fraction of that hundred.
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If you get a ninety percent on your math quiz,
you could have gotten nine points out of ten,
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eighteen points out of twenty, four hundred
fifty out of five hundred, or any other number
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that obeys this ratio of ninety out of a hundred.
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Whatever we have to do to the larger number
to make it one hundred, we do that same thing
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to the other number.
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Ten must be multiplied by ten to get a hundred,
so the nine is also multiplied by ten.
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In this way, percentages are ratios, they
are just very specific ratios that compare
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numbers to a hundred, because although this
number is totally arbitrary, it is an ideal
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size for comparison.
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One hundred is small enough that our brains
can easily comprehend its magnitude, but also
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large enough that there are sufficient gradations
between zero and a hundred so as to make meaningful
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comparisons.
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In this way, we can look at percentages as
simple fractions.
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Eighty percent is eighty one-hundredths.
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We learned how to simplify fractions, so let’s
divide both of these numbers by twenty.
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We should get four fifths.
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This means that eighty percent and four fifths
are equivalent; they mean the same thing.
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Moving to another example, fifty percent is
fifty one hundredths, and dividing both numbers
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by fifty, we get one half.
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This makes sense, as fifty is half of a hundred.
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If you have something like three percent,
that will be three one hundredths, and that
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can’t be simplified any further.
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We should be able to convert between percentages,
fractions, and even decimals in this way with
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relative ease, so let’s check comprehension.
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