JAMB - Mathematics (1994 - No. 2)
The mean of twelve positive numbers is 3. When another number is added, the mean becomes 5. Find the thirteenth number
29
26
25
24
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Let the sum of the 12 numbers be x and the 13th number be y.
\(\frac{x}{12} = 3 \implies x = 36\)
\(\frac{36 + y}{13} = 5 \implies 36 + y = 65\)
\(y = 65 - 36 = 29\)