Let's begin by listing out the information given to us:
11, 16, 11, 15, 9, 10, 11, 13, 15, 17, 10, 14, 17, 10, 13, 15, 11, 12, 12, 12, 11, 12, 14, 15, 15, 13, 10, 15, 12, 11
N = 30
Mean = (11 + 16 + 11 + 15 + 9 + 10 + 11 + 13 + 15 + 17 + 10 + 14 + 17 + 10 + 13 + 15 + 11 + 12 + 12 + 12 + 11 + 12 + 14 + 15 + 15 + 13 + 10 + 15 + 12 + 11) / 30
Mean = 382/30 = 12.7333
Using the standard deviation formula, we have:
σ² = Σ(xi - μ)² ÷ N
σ² = 145.86666666667 ÷ 30
σ² = 4.8622222222222
σ = 2.2050447211388 ≈ 2.21
σ = 2.21
The standard deviation is 2.21