$\"\"$

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The expression is $\"\"$ .

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$\"\"$

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$\"\"$

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Find the sum of the arithmetic sequence by using formula:

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$\"\"$

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$\"\"$ (Substitute 250 for n, $\"\"$ and 750 for $\"\"$ )

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$\"\"$

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$\"\"$

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The sum of the arithmetic sequence is 218,625.