A real estate salesperson has three properties listed for $40,000, $100,000 and $80,000. He thinks that the probability of selling the first listing in November is 1/2. The probabilities of selling the other two listings in November are 1/4 and 3/4 respectively. Determine the probability mass function of the salesperson's November sales (in $). What is the probability that his sales for November will be less than $100,000? Find the mean, variance, and standard deviation of the November sales.