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To find Mean of a Frequency Distribution
Example: The frequency distribution here represents the three-year rate of return of a random sample of 40 small-capitalization growth mutual funds. Approximate the mean three-year rate of return.
|
Class (three- year rate of return) |
Frequency |
|
10.0-14.9 |
7 |
|
115.0-19.9 |
11 |
|
20.0-24.9 |
8 |
|
25.0-29.9 |
6 |
|
30.0-34.9 |
3 |
|
35.0-39.9 |
3 |
|
40.0-44.9 |
0 |
|
45.0-49.9 |
2 |
Press STAT and select 1: Edit. Clear L1 and L2. Enter the midpoints of each class into L1. You can do the calculations for the midpoints directly on this screen. For the first class, type in
(10+14.9)/2 and press ENTER.
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The
value of the midpoint, 12, 45, will appear as the first entry in L1. Continue
this process to obtain the midpoint for each of the classes. Enter the
frequencies into L2. Press STAT and highlight CALC to display the Calc Menu.
Select 1:1-Var Stats and press 2nd.doc_files/image004.gif){kind=small}
,
2nd.doc_files/image006.gif){kind=small}
.
Press ENTER. (Note: You must place the comma between L1 and L2.)
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Using L1 and L2 in the 1:1-Var Stats calculation is necessary when approximating a mean from a frequency distribution. The calculator uses the data in L1 and the associated frequencies in L2 to approximate the average for the dataset. In this example, the approximate mean is 23.2 percent.