Work out the interquartile range (IQR).
Box plots — Notes & Worked Examples Show / Hide
Explanation:
A box plot displays 5 key values: Minimum (left whisker), Lower Quartile (LQ) (left of box), Median (line inside box), Upper Quartile (UQ) (right of box), and Maximum (right whisker). The box width is the IQR = UQ − LQ (middle 50% of data).
When asked to compare two box plots (2 marks), always make two comparisons in context: (1) compare the medians (which group is higher on average), and (2) compare the IQRs or ranges (which group is more consistent / less spread out).
Example 1: A dataset has Minimum = 12, LQ = 20, Median = 28, Range = 35, and IQR = 16. Find the Maximum and UQ to plot the box plot.
Solution:
Example 2: Class A scores: Median = 64%, IQR = 14%. Class B scores: Median = 58%, IQR = 22%. Compare the two classes.
Solution:
Work out the interquartile range (IQR).
Write down the median and work out the interquartile range (IQR).
Worked Solution & Answer
The cumulative frequency graph shows information about the times taken for the 60 students to complete the puzzle.
[INDENT]the least time taken was 24 seconds
[INDENT]the greatest time taken was 96 seconds.
On the grid below, draw a box plot for the distribution of the times taken by the students.
Worked Solution & Answer
The box plot below shows information about the weights of Megan's potatoes.
Give a reason for your answer. [1 mark]
Worked Solution & Answer
Worked Solution & Answer
Worked Solution & Answer
⇒ IQR = 330 – 150 = £180 A1
Worked Solution & Answer
2. The interquartile range of heights is the same for both groups (6 cm), or the range of heights for teenagers (20.5 cm) is greater than for adults (17 cm).
She uses her results to work out the information in this table.
Worked Solution & Answer
Worked Solution & Answer
Max = 154 + 20 = 174 cm A1
The box plot shows information about the finishing times in 2019
@@TABULAR0@@
Use the data to comment on each of the following statements.
• On average, times were faster in 2019 than in 2020
• Times were equally consistent in 2019 and 2020 [4 marks]
Worked Solution & Answer
2019 IQR = 26 – 20 = 6 minutes and 2020 IQR = 27 – 21 = 6 minutes, so the interquartile ranges are equal and times were equally consistent C1
True: 2019 IQR (26 – 20 = 6 min) equals 2020 IQR (27 – 21 = 6 min)