If you have a random sample of 5 numbers, how do you find the sample variance?

To find the sample variance , you need a formula:
sample variance = [ 1 / (n-1) ] * [ Σ x^2 - n*(xbar^2) ]

For example, suppose random samples x = 2 , 10 , 7 , 5 , 18

xbar = ( 2 + 10 + 7 + 5 + 18 ) / 5 = 8.4

Σ x^2 = 2^2 + 10^2 + 7^2 + 5^2 + 18^2 = 502

sample variance
= [ 1 / (n-1) ] * [ Σ x^2 - n*(xbar^2) ]
= ( 1 / 4 ) * ( 502 - 5*8.4^2 )
= 37.3