Working backwards from a mean
Working backwards from a mean to find a missing value, then recalculating the mean after removing a number.
The Question
The mean of five numbers is 14. Four of them are 9, 12, 16 and 20. Find the fifth number. Then find the new mean when the largest number is removed.
The Answer
Reveal the Answer
Total must be 5 × 14 = 70. The four given sum to 57, so the fifth is 13. Removing 20 leaves 9, 12, 13, 16 summing to 50, and 50 ÷ 4 = 12.5. Mean questions are really total questions.
Now watch the solution
Practice Sheet + Marked Answers
The four-question practice sheet, the solutions in our teaching voice and a self-marking quiz for this question are part of The Question Desk course — every school day of the term, with progress you can see. Enrolled group students get it included.
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