Percent of a percent: the SAT math trap

Short answer: Stack percents by multiplying: 0.8 × 0.8 = 0.64. Never add them.

The trap, in one question

Tempting answer: 40%  (20 + 20)

Correct answer: 36%  ($100 × 0.8 × 0.8 = $64)

Watch it in under a minute

How to spot it in 3 seconds

Stack percents by multiplying: 0.8 × 0.8 = 0.64. Never add them.

FAQ

What is the percent of a percent trap on the SAT?

Example: A $100 jacket is 20% off, then another 20% off at checkout. What is the total discount? The tempting answer is 40% (20 + 20); the correct answer is 36% ($100 × 0.8 × 0.8 = $64).

How do you avoid the percent of a percent trap?

Stack percents by multiplying: 0.8 × 0.8 = 0.64. Never add them.

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