An investment portfolio contains stocks of a large number of corporations. Over the last year the rates of return on these corporate stocks followed a normal distribution with mean 13.5% and standard deviation 7.4%.
a. For what proportion of these corporations was the rate of return higher than 19%?
b. For what proportion of these corporations was the rate of return negative?
c. For what proportion of these corporations was the rate of return between 10% and 20%?