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### Course: Grade 7 math (FL B.E.S.T.)>Unit 8

Lesson 4: Measures of variation

Is this some kind of cute cat video? No! Box and whisker plots seek to explain data by showing a spread of all the data points in a sample. The "whiskers" are the two opposite ends of the data. This video is more fun than a handful of catnip. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• What is a quartile?
• a quartile is a quarter of a box plot i hope this helps
• What is the purpose of Box and whisker plots?
• box plots are used to better organize data for easier veiw
• How do you organize quartiles if there are an odd number of data points? Say you have the set: 1, 2, 2, 4, 5, 6, 8, 9, 9. How would you distribute the quartiles? Thanks in advance.
• To divide data into quartiles when there is an odd number of values in your set, take the median, which in your example would be 5. Then take the data below the median and find the median of that set, which divides the set into the 1st and 2nd quartiles. Then take the data greater than the median and find the median of that set for the 3rd and 4th quartiles. In your example, the lower end of the interquartile range would be 2 and the upper end would be 8.5 (when there is even number of values in your set, take the mean and use it instead of the median). So the set would look something like this: 1 2 2 4 5 6 8 9 9. Hope this helps.
• If it is half and half then why is the line not in the middle of the box?
• Because it is half of the Data NOT the number line itself.
• Just wondering, how come they call it a "quartile" instead of a "quarter of"? As far as I know, they mean the same thing. Can someone please explain this?
• The first and third quartiles are descriptive statistics that are measurements of position in a data set. Similar to how the median denotes the midway point of a data set, the first quartile marks the quarter or 25% point. Approximately 25% of the data values are less than or equal to the first quartile. The third quartile is similar, but for the upper 25% of data values. We will look into these idea in more detail in what follows.
• What is the interquartile range
• What is a interquartile?
• The interquartile range is the range of numbers between the first and third (or lower and upper) quartiles. It shows the spread of the middle 50% of a set of data
• What are the 5 values we need to be able to draw a box and whisker plot and how do we find them?
• It has been a while since I've done a box and whisker plot, but I think I can remember them well enough.

You will first need to find the median of your dataset. This can be found by sorting all of your data least-greatest and then finding the middle.
Then, you will find your lower and upper quartiles. The lower quartile can be found by finding the median of the first half of your data - stop at the median you found previously. The upper quartile can be found by finding the median of the second half of your data - start at the median you found previously.
Then you have your minimum and maximum - these are just the smallest and largest values you have in your dataset.