Algebra 1 / Unit 10: Data and Statistics
10.1 Measures of Center and Spread
Notes
- Mean: add the values and divide by how many there are.
- Median: the middle value when the data are in order (average the two middle values if there is an even count).
- Mode: the most common value.
- Range = maximum $-$ minimum. Interquartile range (IQR) = $Q_3 - Q_1$, the spread of the middle half.
- An outlier pulls the mean toward it but barely moves the median, so the median is better for skewed data.
Practice
Find the mean of 4, 8, 6, 10, 7.
$\displaystyle \frac{35}{5} = 7$.
Find the median of 3, 9, 1, 7, 5, 11.
In order: 1, 3, 5, 7, 9, 11. Average 5 and 7.
Salaries at a small company are $40k, $42k, $45k, $47k and $400k. Which best describes a typical salary?
The median is $45k; the mean is about $115k.
Ready for more? Take the Unit 10 test.