WEBVTT

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Here is the problem: sum of 3n minus 1 from n equals 1 to 20.

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Add the terms 3~ n minus 1 for n equals 1, 2, …, 20 (20 terms).

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Write the sum.

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List the first terms.

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Add all 20 terms exactly (as fractions).

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So the answer is 610.

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Each term is computed exactly and added. For long arithmetic or geometric sums a closed formula gives the same result.

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Decimal value: 610.