SAT Percentages study notes

A percent is always a percent of some base. For percent change, that base is the original value. For two changes in a row, multiply the factors; a 20% decrease followed by an 8% increase is not simply a 12% decrease.

Worked example

After a 20% discount and then 8% tax, a jacket costs $86.40. What was its original price?

The price was multiplied by 0.80 and then 1.08, for a combined factor of 0.864. Divide 86.40 by 0.864 to get $100.

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