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JAMB 1994 · UME · Q45

The mean of twelve positive numbers is 3. When another number is added, the mean becomes 5. Find the thirteenth number.

Worked solution (try it first)
  1. Total of the twelve numbers: 12×3=3612 \times 3 = 36.
  2. Total of all thirteen: 13×5=6513 \times 5 = 65.
  3. The thirteenth number is the difference: 65−36=2965 - 36 = 29, option A.

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