Average = (2 + 6 + 7 + 10 + 10)/5 = 35/5 = 7
x - mean, square.
2 - 7 = -5, -5² = 25
6 - 7 = -1, -1² = 1
7 - 7 = 0, 0² = 0
10 - 7 = 3, 3² = 9
10 - 7 = 3, 3² = 9
Sum of square = 25 + 1 + 0 + 9 + 9 = 44
Variance = 44/5 = 8.8
Standard deviation = √variance = √8.8 ≈ 2.966