Month: April 2017

μ= 1/n Σi Xi
σ^2 = 1/n Σ(xi – μ)^2

σ^2 = ΣXi^2/N -　(ΣXi)^2/N^2

3,4,5,6,7
N = 5
ΣXi = 25
ΣXi^2 = 135

μ= 2
σ^2 = 2

Variance: spread of data
standard deviation

17, 19, 18, 17, 19 -> mean=18
-1 1 0 -1 1
variance = 0.8
std deviation = 0.8944

7, 38, 4, 23, 17 -> mean=18
-11 20 -14 5 0
variance = 148.4
std deviation = 12.18

mean = μ
variance
1/n Σ(Xi – μ)^2

standard deviation = √variance

data 3,4,5,6,7
mean 5
variance 2
std dev 1.414

data 8, 9, 10, 11, 12
mean 5
variance 2
std dev 1.414

data 15, 20, 25, 30, 35
mean 25
variance 50
std dev 7.071

MEAN, MEDIAN, MODE

house prices
190k 170k 165k 180k 165k
Mean = 1/N ΣXi = 175

Median
picks the one in the middle

Mode
most frequently used number

3, 9, 3, 8, 2, 9, 1, 9, 2, 4
mean = 5
median = 3, 4
mode = 9