$\"\"$

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The given values $\"\"$ .

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Where $\"\"$ is the first term and $\"\"$ is the common difference. \ \

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The sum of an arithmetic series $\"\"$ .

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$\"\"$ (Substitute $\"\"$ )

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Apply multiplication property of equality: a = b then $\"\"$ .

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$\"\"$ (Multiply each side by 2)

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$\"\"$ (Cancel common terms)

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$\"\"$ (Multiply: $\"\"$ ) $\"\"$

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Apply division property of equality: a = b then $\"\"$ .

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$\"\"$ (Divide each side by 31)

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$\"\"$ (Cancel common terms)

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

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Apply subtraction property of equality: a = b then $\"\"$ .

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$\"\"$ (Subtract 78 from each side)

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

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Substitute $\"\"$ , n = 31 and $\"\"$ in $\"\"$ .

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$\"\"$

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

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$\"\"$ (Multiply: $\"\"$ )

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Apply multiplication property of equality: a = b then $\"\"$ .

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

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$\"\"$ (Cancel common term)

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$\"\"$ (Multiply: $\"\"$ ) $\"\"$

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Apply addition property of equality: a = b then $\"\"$ .

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$\"\"$ (Add 24 to each side)

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$\"\"$ (Add: $\"\"$ )

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Apply division property of equality: a = b then $\"\"$ .

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$\"\"$ (Divide each side by 30)

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$\"\"$ (Cancel common terms)

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d = 3 (Divide: $\"\"$ )

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The 1st term is $\"\"$ and 2nd term is a + d = $\"\"$ ,

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3rd term is a + 2d = $\"\"$ . $\"\"$

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The first three terms of the series is $\"\"$ .