Page 159 - Probability Demystified

148 CHAPTER 9 The Normal Distribution

Measures of Average

There are three statistical measures that are commonly used for average.
They are the mean, median, and mode. The mean is found by adding the data
values and dividing by the number of values.

EXAMPLE: Find the mean of 18, 24, 16, 15, and 12.
SOLUTION:

Add the values: 18 þ 24 þ 16 þ 15 þ 12 ¼ 85
Divide by the number of values, 5: 85 5 ¼ 17
Hence the mean is 17.

EXAMPLE: The ages of 6 executives are 48, 56, 42, 52, 53 and 52. Find the
mean.
SOLUTION:

Add: 48 þ 56 þ 42 þ 52 þ 53 þ 52 ¼ 303
Divide by 6: 303 6 ¼ 50.5
Hence the mean age is 50.5.

The median is the middle data value if there is an odd number of data
values or the number halfway between the two data values at the center, if
there is an even number of data values, when the data values are arranged in
order.

EXAMPLE: Find the median of 18, 24, 16, 15, and 12.

SOLUTION:
Arrange the data in order: 12, 15, 16, 18, 24
Find the middle value: 12, 15, 16, 18, 24
The median is 16.

EXAMPLE: Find the median of the number of minutes 10 people had to wait
in a checkout line at a local supermarket: 3, 0, 8, 2, 5, 6, 1, 4, 1, and 0.
SOLUTION:
Arrange the data in order: 0, 0, 1, 1, 2, 3, 4, 5, 6, 8
The middle falls between 2 and 3; hence, the median is (2 þ 3) 2 ¼ 2.5.