Practice Interquartile Range (IQR) in Statistics
Use these practice problems to test your method after reviewing the concept explanation and worked examples.
Quick Recap
The range of the middle 50% of data, calculated as Q_3 - Q_1. It measures spread while ignoring extreme values.
IQR focuses on where most of the data lives, ignoring the extremes. If regular range is how far the outliers stretched, IQR is how wide the main crowd is. More resistant to outliers than range.
Example 1
easyGiven the data set: 4, 7, 9, 12, 15, 18, 22, 25, 30, find the interquartile range (IQR).
Example 2
mediumTest scores: 55, 60, 65, 70, 72, 75, 78, 80, 85, 90, 95. Find the IQR and use it to determine the boundaries for outliers using the 1.5 \times IQR rule.
Example 3
mediumTwo classes took the same test. Class A: Q_1 = 60, Q_3 = 80. Class B: Q_1 = 70, Q_3 = 90. Which class has greater consistency in scores? Explain using the IQR.
Example 4
hardDaily temperatures (°C) for two weeks: 15, 16, 14, 18, 20, 22, 19, 35, 17, 16, 18, 21, 20, 19. Find the IQR and use the 1.5 \times IQR rule to identify any outliers. Then recalculate the mean with and without the outlier(s).