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Find the average of the first 20 natural numbers?

Correct answer: D. 10.5

  • A. 10
  • B. 11.5
  • C. 12
  • D. 10.5

Explanation

The first 20 natural numbers are 1 through 20, whose average is the midpoint of the first and last terms: (1 + 20) / 2 = 10.5. The likely trap is 10, which comes from using 20 / 2 and overlooking that the sequence starts at 1.

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About Averages

An average represents the total of a set of values divided by the number of values, and a weighted average gives different importance to different groups. Problems involve missing values, combined averages, replacement of observations, and changes in the average, so the total and count must be tracked separately.

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