ShmoopTube

00:03

Here's a shmoopy question for you...

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Unlike his shady friend Dishonest Paul, Honest John actually pays for songs from iTunes.

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He pays for x number of songs at a total cost of $12.50.

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At this rate, what is the total cost of 10 songs?

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Here are the potential answers...

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Alright, hit pause. Try it yourself.

00:29

OK, this question is testing whether we know the business formula for cost...

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...or a fancy way of asking us to calculate the unit price times a quantity.

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The formula looks like this:

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Price times quantity equals total cost.

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Well, we know the base elements here...

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Price times number of songs equals $12.50.

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So we can set up the equation... px equals 12.5

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We should isolate p in the equation because we'll want to use p later to find the total

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cost of 10 songs...or 10p.

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To isolate p, we can divide x from both sides of the equation... getting p equals 12.5 over x.

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Remembering that we want to find 10p...

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we can multiply 10 times 12.5 over x to get 125 over x.

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And it looks like our answer is B.

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Of course, if your name is Dishonest Paul, you already knew that.

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