Dispersion and standard deviation
Answers are for parents and teachers.
1
Find the range, Q₁, Q₂, Q₃ and IQR of 2, 5, 8, 9, 13, 14, 20.
Range 18; Q₂ = 9; Q₁ = 5; Q₃ = 14; IQR = 9.
2
Find σ for 2, 3, 5, 7, 8 to 2 decimal places.
Mean 5; squares 9, 4, 0, 4, 9 add to 26; σ = √5.2 ≈ 2.28.
3
Scores x = 2, 3, 4, 5 with frequencies 1, 2, 4, 3. Find the mean and σ.
Mean 3.9; Σ f(x − x̄)² = 8.9; σ = √0.89 ≈ 0.94.
4
Classes 0–, 10–, 20–, 30– with f = 3, 6, 7, 4. Find σ.
Centres 5, 15, 25, 35; mean 21; Σ f(x − 21)² = 1880; σ = √94 ≈ 9.70.
5
Two bakeries make bread weighing on average 500 g. Bakery 1 has σ = 4 g and bakery 2 has σ = 12 g. Which sells more even loaves, and why?
Bakery 1: its σ is smaller, so the weights are closer together.