Explanation needed to the quiz question

3 , 2

Johnny wanted to know how many days per week people in his class exercise, so he asked 3 of his friends

-class = population  and 3 friends = simple

The answers he got were 1, 3 and 5.

so you have (1,3,5)

mean = 1+3+5 / 3 = 3       *you are working with simple so mean = x̄ 

variance = 8

standard deviation = 2    *you are working with simple so standard deviation= s

as here the value of mean is 3 from the formula of variance =4 when dividing by (n-1) [* As this is a sample]

hence , standard deviation= 2

μ represents the population mean.
σ represents the population standard deviation.
xˉ represents the sample mean.
s represents the sample standard deviation.
Given Johnny's sample:

Sample mean xˉ=1+3+5/3=9/3=3
Sample standard deviation s=√(1−3)^2+(3−3)^2+(5−3)^2/3−1=

√4+0+4/2=√8/2=√4

=2

so xˉ=3, s=2