The rates of return of ten stocks are normally distributed with mean μ = 2 and standard deviation σ = 4 (units are percentages). Rates of return are independent from stock to stock. Each stock sells for $10 a share. Amy, Bill, and Carrie have $100 each to spend on their stock portfolio. Amy buys one share of each stock. Bill buys two shares from five different companies. Carrie buys ten shares from one company. For each person, find the probability that their average rate of return is positive.