☰ Year plan · Statistics

Quartiles from frequency tables

Week 8 · Quartiles from a frequency table: ascending cumulative frequency, the quartile class and the formula, and the graphical method · 3 lessons
Answers are for parents and teachers.
1
The ages of 80 members of a sports club are in the classes 20–, 30–, 40–, 50–, 60–70 with frequencies 9, 21, 28, 16, 6. Build the cumulative column and find Q₁, Q₂ and Q₃.
2
Heights of 40 seedlings in cm: classes 10–, 20–, 30–, 40–, 50–60 with frequencies 5, 9, 13, 8, 5. Find the three quartiles with the formula.
3
The curve shows the daily steps, in hundreds, of 60 walkers. Read Q₁, Q₂ and Q₃ (orders 15, 30 and 45). The table behind it has the classes 0–, 20–, 40–, 60–, 80–100 with frequencies 6, 14, 20, 12, 8: check one of your readings with the formula.
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4
A pupil has 50 values in a frequency table and finds the orders (50 + 1) ÷ 4 = 12.75, 25.5 and 38.25. What should she use instead, and what are the orders?
5
A table has the classes 0–, 10–, 20–30 with frequencies 10, 20 and 10. Find the three quartiles. Notice what happens with the order 10.