TalkingPencil

Find the inter-quartile range of a set of data

Follow this one with me, a step at a time. Try to guess each step first.
Worked example 1

Find the inter-quartile range of the following data: 57, 33, 25, 20, 42, 36, 54, 46. Take the lower and upper quartiles as the medians of the lower four and the upper four data.

Remember: Put the data in order first. Each quartile is the median of one half, here the mean of the two middle values of four.

Common mistakes

  • Used the median in place of a quartile.
  • Gave the range, the largest value minus the smallest. The inter-quartile range uses the quartiles.
  • Gave the upper quartile. The inter-quartile range is the upper quartile minus the lower quartile.