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How to Calculate Interquartile Range From a Box & Whisker Graph

A box and whisker graph is one way to visually represent information from a data set. A box is drawn to represent the data between the 25th and 75th percentiles. The lower extreme and upper extreme are represented by dots. Lines are drawn from these extremes to connect to the box, hence the name "box and whisker graph." From these graphs, you can easily figure the inter-quartile range, which represents the span between the 25th percentile and the 75th percentile.

Instructions

- 1
  Find the lower quartile of the box and whisker graph by locating the left hand side of the box and finding the number over which it appears. For example, if the left hand side of the box appears over "25" on the graph, "25" is the lower quartile of the data.
- 2
  Find the upper quartile of the box and whisker graph by locating the right hand side of the box and finding the number over which it appears. For example, if the right hand side of the box appears over "60" on the graph, "60" is the upper quartile of the data.
- 3
  Subtract the lower quartile from the upper quartile to find the inter-quartile range based on the box and whisker graph. In this example, subtract 25 from 60 to find the inter-quartile range equals 35.

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