So let's say we have a bag that has 5 balls marked with numbers 2 2 2 3 3. One of the ball got lost, but we don't know which. The probability of the lost ball is random, so it can ether be 3/5 or 2/5 depending on the mark. Then we take a random ball from the urn, X is its' number. Whats the random variable mean of this X?

As far as I think, we have scenarios where we pick a ball and its' number is 2 and probability is 2/4, then number 2 again probability 3/4, then number 3 with probability of 2/4 and number 3 with probability of 1/4. 

We do 2\*2/4+2\*3/4+3\*2/4+3\*1/4, is this the correct way or do we need to add probabilities of which ball might be lost, so we add 3/5 or 2/5?