Multiple choice general knowledge math & puzzles

What is the sum of all positive integers that are multiples of 7 from 200 to 400?

  1. 8729

  2. 8700

  3. 8624

  4. 8500

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A Correct answer
Explanation

Multiples of 7 from 200 to 400 are: 203, 210, ..., 399. This is an arithmetic series with first term 203, last term 399, common difference 7. Number of terms = (399 - 203)/7 + 1 = 28 + 1 = 29. Sum = (29/2) × (203 + 399) = 29 × 301 = 8729.