# Thread: Probability Mass Function Question

1. ## Probability Mass Function Question

The P.M.F. (probability mass function) of a discrete random variable X is given by,
f(x)=c ((x^2)+4), where X = (0,1,2,3), and c is a constant.

a) Determine value of c.
b) Find the mean and variance of X.

Does anyone know how to answer this?

2. Originally Posted by abc4616
The P.M.F. (probability mass function) of a discrete random variable X is given by,
f(x)=c ((x^2)+4), where X = (0,1,2,3), and c is a constant.

a) Determine value of c.
The total probability should sum to 1, so:

f(0)+f(1)+f(2)+f(3)=1

so:

c{(4)+(5)+(8)+(13)}=1

Which you should be able to solve.

b) Find the mean and variance of X.
mean=sum[ n f(n), n=0,1,2,3]

variance=sum[ (n-mean)^2 f(n), n=0,1,2,3]

so you are left with the arithmetic.

RonL