The average of five results is 46 and that of the first four is 45. The fifth result is__________?
Correct answer: D. 50
- A. 1
- B. 10
- C. 12.5
- D. 50
Explanation
The five results total 5 x 46 = 230, and the first four total 4 x 45 = 180. Therefore the fifth result is 230 - 180 = 50. The likely trap is 10, which comes from subtracting the two averages without multiplying them by their respective numbers of results.
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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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