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The average of 35 students in a class is 16 years. The average age of 21 students is 14. What is the average age of remaining 14 students?

Correct answer: D. 19 years

  • A. 15 years
  • B. 17 years
  • C. 18 years
  • D. 19 years

Explanation

The total age of 35 students is 35 x 16 = 560 years, while the 21 students contribute 21 x 14 = 294 years. The remaining 14 students therefore have a total age of 560 - 294 = 266 years, giving an average of 266 / 14 = 19 years. A student may choose 18 years by subtracting the two given averages without weighting them by their group sizes.

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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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