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Here is the problem: Five times a number minus 4 equals 21. What is the number?

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Let x be the number: “5 times a number minus 4” becomes (5) times x minus 4.

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Read the problem. Let x be the unknown number. “5 times a number minus 4 is 21” translates to (5) times x minus 4 equals 21.

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Solve the linear equation. 5x minus 4 equals 21 → x equals (21 plus 4) / 5 equals 5.

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So the answer is The number is 5.

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Let x be the number: “5 times a number minus 4” becomes (5) times x minus 4.

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Substitute x equals 5: (5) times (5) minus 4 equals 21, which checks out.