I have a graph of the probability distribution function of a scalar random variable X and I need to compute E(X).

[plovplov]

Hi. Please help. I have a graph of the probability distribution function of a scalar random variable X and I need to compute E(X). The answer should be 0,1666, but I don't understand how to get that. As far as I know, for discrete variable we mutiply values and probabilities and then sum up, but it results into (-1)*(1/3)+(1/2)*(2/3)+1*1 = 1. What am I doing wrong?

 

[blamocur]

Hi. Please help. I have a graph of the probability distribution function of a scalar random variable X and I need to compute E(X). The answer should be 0,1666, but I don't understand how to get that. As far as I know, for discrete variable we mutiply values and probabilities and then sum up, but it results into (-1)*(1/3)+(1/2)*(2/3)+1*1 = 1. What am I doing wrong? View attachment 36436

The graph you have is a cumulative distribution function, not a probability density function (also called probability mass function for discrete random variables). Do you know how to get from one to another?

(Note that you use probabilities 1/3, 2/3 and 1, which do not add up to 1.)