AlgebraHardNumber removed from a list, from two averages
Algebra practice question
The average (arithmetic mean) of five numbers is 12. When one of the numbers is removed, the average of the remaining four is 10. What is the number that was removed?
Answer: 20
The five total 60; the four total 40; the removed number is 60 − 40 = 20.
Common wrong answers
- If you answered 2
- 2 is the change in the average, not the number.
- If you answered 12
- 12 is the original average.
- If you answered 22
- 22 adds the two averages.
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