The population is too small to assume independence.
Once again Y can have three values.
A shipment of 20 parts contains 2 defectives. Two parts are chosen at random from the shipment and checked. Let the random variable Y denote the number of defectives found. Find the probability function of this random variable. Find mean and variance of random variable Y.
As to the notation is the combination of twenty items taken two at a time. That is the number of ways to pick two representatives from twenty individuals. If Y=1 we select one defective from two and one good from eighteen.