STA006 · Probability & statistics · Classes 9–11
Quartiles
Quartiles split ordered data into four equal parts: Q₁ is the median of the lower half, Q₂ the median, Q₃ the median of the upper half.
Q₁ Q₂ Q₃Quartiles
📐 Formula
Q₁ = median of lower half; Q₃ = median of upper half
✏️ Worked example
2, 3, 3, 5, 7, 8, 9: lower half 2, 3, 3 → Q₁ = 3; Q₂ = 5; upper half 7, 8, 9 → Q₃ = 8.
🌍 Where it is used
Growth charts (percentiles), exam score bands.
❓ Quick check
Q₂ is the same as the…
🏋️ Practice
EasyQ₁ of 1, 2, 3, 4, 5, 6, 7?
Answer: 2
MediumQ₃ of 1, 2, 3, 4, 5, 6, 7?
Answer: 6
ChallengeWhat fraction of data lies below Q₃?
Answer: ¾