In a box-and-whisker plot, the interquartile range is a measure of the spread of the middle half of the data. Find the interquartile range for the data set: 10, 3, 7, 6, 9, 12, 13

In statistics, it is imperative to arrange your data entries from least to greatest. That would be the first step of our solution

3 6 7 9 10 12 13

Interquartile range is the difference of the last quartile to the first quartile. Divide your entire data set into four parts. Each division is called a quartile. Its numerical value is the average of its numbers. However, since our data set contains 7 numbers, which is odd, we write the median (middle value) twice. The quartiles are:

3 6 | 7 9 | 9 10 | 12 13

Q₁ = (3+6) / 2 = 4.5

Q₂ = (7+9) / 2 = 8

Q₃ = (9+10) / 2 = 9.5

Q₄ = (12+13) / 2 = 12.5

The interquatile range is Q₄ - Q₁ = 12.5 - 4.5 = 8