Alissa Fong

MA, Stanford University
Teaching in the San Francisco Bay Area

Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts

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Percent Change - Problem 3

Alissa Fong
Alissa Fong

MA, Stanford University
Teaching in the San Francisco Bay Area

Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts

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One of the tools of mathematicians is moving from a concrete example into the abstract, or general case, which is what we practice here. We don't know the initial value, so we can call it x. If we want it to increase by 20%, we write 20% as 0.2 and write the new value as x + 0.2x . From there, we want that value to decrease by 20%, so we subtract 0.2 (x + 0.2x) . This will tell us whether increasing any value by 20% and then decreasing again by 20% gives the original number (and we see here that it doesn't.)

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