Step 1: Recall the mean definition and look at the given information.

NOTE: The mean (or arithmetic mean) of n observations (variates)

n is given by x_1, x_2, x_3, x_4..................x_n

Mean = \frac{\text{ Sum of the variables}}{\text{Total number of variables}}

= \frac{x_1+x_2+x_3+x_4.............x_n}{n}

(Mean: The mean is the average of the numbers. You find the mean by

adding the numbers together and then dividing by the number of numbers

in the group.)

Step 2: Count how many numbers are in the group.

12, 10, 15, 10, 16, 12, 10, 15, 15, 13

There are 10 numbers

Step 3: Add all the numbers together

12 + 10 + 15 + 10 + 16 + 12 + 10 + 15 + 15 + 13 = 128

Step 4: Now divide the sum by the number of numbers

Mean = \frac{128}{10}

The mean = 12.8