# Chapter 3

```Chapter 3
Numerical Descriptions of Data
Section 3.1
Measures of Center
Mean
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Add up all data values, then divide by the total number of data values.
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Example
1+2+3+4+5
5
=3
ROUNDING RULE: round to one more decimal place than the highest number of
decimal places contained in the data
Weighted Mean
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Multiply each data value by its “weight” then divide by the sum of the
weights. Think “per what?” to determine what the weight is.
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Example:
Class
Hours
Weight
Math
3
B
3
English
3
A
4
History
3
C
2
Science
3
A
4
PE
3
F
0
ππππβπ‘ππ ππππ = πΊππ΄
3 3 + 3 4 + 3 2 + 3 4 + 3(0)
=
15
9 + 12 + 6 + 12 + 0 39
=
=
= 2.6
15
15
Solution:
a. 3
b. 2.5
Solution:
no mode,
unimodal,
bimodal
Section 3.2
Measures of Dispersion
Calculator Directions
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Press STAT
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Press edit
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In L1 insert data values. If you need to clear data, press up to highlight L1, press clear (not delete), and
press down.
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Press 2nd quit (mode)
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Press STAT
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Arrow over to CALC
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Press 1-Var Stats
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On the home screen, press 2nd L1 (1)
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Press enter
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You will then see a list of items.
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π₯ = ππππ
ππ₯ = π πππππ π π‘ππππππ πππ£πππ‘πππ
ππ₯ = ππππ’πππ‘πππ π π‘ππππππ πππ£πππ‘πππ
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To find the variance, you will square the standard deviation.
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If you scroll down you will see the max, min, and median.
```