Watch out
Subtracting in the wrong order.
Scottish National 5 Mathematics
National 5 Maths Interquartile range
Determine quartiles and use the interquartile range to compare the spread of data.
Formula reference
Check the National 5 rules and formulae linked to this topic.
Which method?
Match exam clues to a suitable method.
Before you start
- Order raw data before locating quartiles.
- Decide whether a calculator supports the method; exact working may still be required.
- Read the command word, record the units or requested form, and make the final answer match it.
Explanation
Interquartile range is an assessed part of Scottish National 5 Mathematics in the statistics area. Determine quartiles and use the interquartile range to compare the spread of data.
Order raw data before locating quartiles.
Apply the stated or site-standard quartile convention consistently.
Subtract Q1 from Q3 and interpret a smaller IQR as less spread in the middle half.
The interactive bank below mixes direct skills, reverse questions, interpretation and contextual reasoning rather than repeating one number pattern.
Key formulae and rules
- IQR = Q3 − Q1
Check
Check the calculation, then state what the result means for the named data or model rather than treating an estimate as exact.
Exam tip
Quote the relevant statistic or model value, then interpret it in the context of the named data.
Worked examples
Worked example 1
Interquartile range worked example
A data set has Q1 = 14 and Q3 = 29. Find the IQR.
- IQR = Q3 − Q1
- 29 − 14 = 15
Answer: 15
Watch out
- Subtracting in the wrong order.
- Comparing centre when the question asks about spread.