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Here is the problem: Half of a number is 9. What is the number?

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Let x be the number: “half of a number” becomes (1 over 2) times x.

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Read the problem. Let x be the unknown number. “half of a number is 9” translates to (1 over 2) times x equals 9.

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Solve the linear equation. 0.5x plus 0 equals 9 → x equals (9 minus 0) / 0.5 equals 18.

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So the answer is The number is 18.

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Let x be the number: “half of a number” becomes (1 over 2) times x.

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Substitute x equals 18: (1 over 2) times (18) equals 9, which checks out.