Answer:
The unknown number is 16
Step-by-step explanation:
Let the missing number be x
To find the mean we add up all the numbers and divide by the number of numbers
21, 11, _x_, 27, 22, 13, 16
We know the mean is 18
(21+ 11+x +27+ 22+ 13+ 16)/7 = 18
Multiply each side by 7
(21+ 11+x +27+ 22+ 13+ 16)/7 *7 = 18*7
(21+ 11+x +27+ 22+ 13+ 16) = 126
Combine like terms
110+x = 126
Subtract 110 from each side
110+x-110 = 126-110
x = 16
