3
=
+
+
+
=
∑
=
=
10
...
10
2
10
1
x
x
i
i
Example 4.1 (pg. 98)
The reported time on the Internet of 10 adults are 0, 7, 12, 5, 33,
14, 8, 0, 9, 22 hours. Find the mean time on the Internet.
22
11.0
The Arithmetic Mean
Example 4.2 (pg. 98)
Suppose the telephone bills represent
the
population
of measurements.
The population mean is
=
+
+
=
∑
=
μ
=
200
...
200
x
i
200
1
i
42.19
38.45
45.77
43.59
Example 4.3 (pg99)
±
The
Median
of a set of observations is the value that
falls in the middle when the observations are
arranged in order of magnitude.
The Median
Comment
Odd number of observations
9, 12, 14, 22
, 12, 14, 22, 33
0, 0, 5, 7,
8, 9,
12, 14, 22, 33
Even number of observations
Find the median of the time on the internet
for the 10 adults of example 4.1
Suppose only 9 adults were sampled
(exclude, say,
the longest time (33))
8.5,
8
±
The
Mode
of a set of observations is the value that
occurs most frequently.
±
Set of data may have one mode (or modal class), or
two or more modes.
The Mode
The modal class
For large data sets
the modal class is
much more relevant
than a single-value
mode.