3. On any given day 20 customers go to Computerland to shop for a PC. The chance that any one of the customers will purchase a computer is 0.3. Assume that the customers' purchase decisions are independent and that a customer who buys will only buy one computer. What is the least amount of stock Computerland needs to have on hand at the beginning of a day so that the probability of a shortage (demand exceeding supply) will be at most 0.025?