AlgebraEasy–MediumFifth number from a known mean
Algebra practice question
The mean of five numbers is 12. Four of the numbers are 9, 10, 15, and 17. What is the fifth number?
Answer: 9
The five numbers total 5 × 12 = 60. The four given total 51, so the fifth is 60 − 51 = 9.
Common wrong answers
- If you answered 12
- 12 assumes the fifth equals the mean.
- If you answered 51
- 51 is the total of the four given numbers.
- If you answered 12.75
- 12.75 is the mean of the four given numbers.
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