The average of first ten prime numbers which are odd is____________?
Correct answer: C. 15.8
- A. 12.9
- B. 13.8
- C. 15.8
- D. 17
Explanation
The first 10 odd prime numbers are 3, 5, 7, 11, 13, 17, 19, 23, 29 and 31. Their sum is 158, so the average is 158/10 = 15.8. The likely mistake is choosing 13.8, usually caused by omitting one of the larger primes or adding the list incorrectly.
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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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