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Here is the problem: A shirt costs 40 and is 25 percent off. What is the sale price?

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The original price is 40 and it decreases by 25 percent, so the percent change is negative 25 percent. Percent increase or decrease; old equals 40, p equals negative 25 percent; solve for new.

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Read the problem. The original price is 40 and it decreases by 25 percent, so the percent change is negative 25 percent.

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Identify the known values. Percent increase or decrease. Known: old equals 40, p equals negative 25 percent. Unknown: new value (new).

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Write the equation. new equals old times (1 plus p/100).

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Solve for new. new equals 40 times (1 plus negative 0.25).

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Result. new equals 30.

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So the answer is New price equals 30 (the discount is 10).

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Substitute the known values into new equals old times (1 plus p/100) and isolate new. Keep units consistent (for example miles, miles per hour and hours).

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Substituting new equals 30 back into new equals old times (1 plus p/100) balances both sides, which checks out.