Answer:
missing number = 7
Explanation:
The mean is the average of a set of data points and we find it by dividing the sum of all the data points by the total number of points.
We can allow m to represent the unnown number. Since there are 4 data points in all and we know that the mean is 9, we cause the following formula to solve for m, the missing number:
9 = (6 + m + 11 + 12) / 4
36 = m + 29
7 = m
Thus, in order to have a mean of 9 given the data set already contains the numbers 6, 11, and 12, the value of the missing number must be 7