Multiple choice

Find the sum of the first 20 terms of the arithmetic series if $a_{1} = 10$ and $a_{20}=100$.

  1. 1000

  2. 1100

  3. 1200

  4. 1300
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B Correct answer
Explanation

The sum of an arithmetic series is given by S = (n/2) * (a1 + an). With n = 20, a1 = 10, and a20 = 100, the sum is (20/2) * (10 + 100) = 10 * 110 = 1100.

AI explanation

Using the formula for the sum of an arithmetic series, S = n/2 * (a1 + an). Plugging in the given values gives S = 20/2 * (10 + 100), which is 10 * 110. The sum of the first 20 terms is 1100.

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