Answer: 28
Step-by-step explanation:
The mean of 15 numbers = 12
Then , the sum of the numbers = 12x15 = 180
Let the extra number included be [tex]x[/tex] , then
The new sum = [tex]x + 180[/tex]
And the new total number will increase from 15 to 16
new mean = 13 , so we have :
[tex]\frac{x+180}{16} = 13[/tex]
[tex]x+ 180 = 16(13)[/tex]
[tex]x + 180 = 208[/tex]
[tex]x = 208 - 180[/tex]
[tex]x = 28[/tex]
therefore , the extra number is 28
