Interquartile range is Q1 - Q3. Say you have the data set 4,3,6,8,10. Your median is your middle number. In this case that number is 6. Now Q1 - 4 and 3. You have to add 4 and 3. Well, that's 7. So, now Q3 - 8 and 10. 8 + 10 = 18. Now subtract 18 from 7 and you get 11. So, your Interquartile range is 11 units.
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