# Statistics

Values that are used to describe the center of a set of data are mean, median, and mode. The mean is the average.   The median is the middle number.   The mode is the number that occurs most often.

The range, mean absolute deviation, and interquartile range are all ways to measure the variability for a set of data.

• The range measures how spread out the data is.   To find the range, subtract the smallest value from the largest value in a set of data.
• The mean absolute deviation (MAD) is the average distance of each data value from the mean.
• The  interquartile range (IQR)  is the difference between the first and third quartiles.

A stem-and-leaf plot, histogram, line graph, and frequency table are all graphic representations of data.  Graphs can be used to analyze the data and find measures of center and variability.  Graphical displays of data can also be helpful when comparing two or more sets of data.

## Practice

Use this data to find what’s requested.

### 21 24 27 29 31 34 39 42

1) Find the Range of the data.

2) Find the 1st Quartile of the data.

3) Find the 2nd Quartile of the data.

4) Find the 3rd Quartile of the data.

Use this data to find what’s requested.

### 4 5 7 8 8 9 10 11 12 12

5)  Find the mode.

6)  Find the median.

7)  Find the mean.

8)  Find the range and MAD (Day 41) for this set of data. 0, 63, 34, 0, 1, 27, 2, 13

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