An arithmetic progression has first term and common difference . Find the sum of the first 20 terms.

Answer and explanation

Correct answer: B. 860

  1. Step 1: . Step 2. . Answer: 860. Why not the others: 1620: That multiplies the last term by instead of using the average of the first and last. 81: That is only the 20th term. 864: That is off by one common difference.

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An arithmetic progression has first… | Singapore GCE A-Level