$\"\"$ $\"\"$ $\"\"$

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Let n represent the number.

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The word “equals” can be represented as “=” symbol.

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The word “decreased” indicates subtraction and the symbol is “ $\"\"$ ” .

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The word “twice the number” can be represented as “2n” $\"\"$

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Rewrite the sentence into expression as

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$\"\"$

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The expression is $\"\"$ . $\"\"$

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According to subtraction property of equality:Subtract 12 from each side.

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$\"\"$

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$\"\"$ (Apply commutative property of addition: $\"\"$ )

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$\"\"$ (Apply additive inverse property: $\"\"$ )

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$\"\"$ (Apply additive identity property: $\"\"$ )

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$\"\"$ (Subtract: $\"\"$ ) $\"\"$

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According to division property of equality:Divide each side by 2.

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$\"\"$

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$\"\"$ (Cancel common factors)

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$\"\"$ (Divide: $\"\"$ )

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$\"\"$ (Multiply each side by negative one) \ \

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$\"\"$ (Product of two same signs is positive) \ \

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$\"\"$

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The number is $\"\"$ .