Mia bought a poster that was discounted $5 from an original price of $20. Which equation models how Mia can find the percent of discount?

Let x represent the discount as a decimal. The discount amount equals the original price multiplied by the discount rate, so the equation is $5 = $20(x). This matches choice C; for example, solving gives x = 5 ÷ 20 = 0.25, or a 25% discount.

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