Problem-Solving and Data AnalysisVery hardValue that raises a mean
Problem-Solving and Data Analysis practice question
A list of 7 numbers has a mean of 12. When an eighth number is added to the list, the mean of the 8 numbers is 13. What is the eighth number?
Answer: 20
The 7 numbers total 84; the 8 numbers total 104. The eighth is 104 − 84 = 20.
Common wrong answers
- If you answered 1
- 1 is the change in the mean, not the number added.
- If you answered 8
- 8 adds 1 to 7, confusing counts with values.
- If you answered 13
- 13 assumes the new number equals the new mean; it must be higher to pull the mean up.
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