Understanding Quartiles and Interquartile Range
Part of Range & IQR · GCSE GCSE Mathematics revision
This deep dive covers Understanding Quartiles and Interquartile Range within Range & IQR for GCSE Mathematics. Revise Range & IQR in Statistics for GCSE Mathematics with 12 exam-style questions and 20 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 4 of 8 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 4 of 8
Practice
12 questions
Recall
20 flashcards
Understanding Quartiles and Interquartile Range
Finding Quartiles
Step 1: Arrange data in ascending order
Step 2: Find the median (Q2)
Step 3: Find Q1 (median of lower half)
Step 4: Find Q3 (median of upper half)
Detailed Example: Finding Quartiles
Data: 12, 15, 18, 22, 24, 28, 30, 35, 38
Step 1: Already in order: 12, 15, 18, 22, 24, 28, 30, 35, 38
Step 2: Q2 (median) = 24 (5th value of 9)
Step 3: Lower half: 12, 15, 18, 22 → Q1 = (15 + 18) ÷ 2 = 16.5
Step 4: Upper half: 28, 30, 35, 38 → Q3 = (30 + 35) ÷ 2 = 32.5
Calculating IQR
IQR = Q3 - Q1 = 32.5 - 16.5 = 16
What IQR Tells Us
The IQR represents the spread of the middle 50% of the data. It's not affected by outliers, making it more reliable than range when extreme values are present.
Keep building this topic
Read this section alongside the surrounding pages in Range & IQR. That gives you the full topic sequence instead of a single isolated revision point.
Practice Questions for Range & IQR
The range of a set of data is calculated by:
Explain why the interquartile range (IQR) is sometimes preferred over the range as a measure of spread.
Quick Recall Flashcards
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