An investment portfolio contains stocks of a large number of corporations. Over the last year the rates of return on

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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 12.2% and standard deviation 7.2%. 

For what proportion of these corporations was the rate of return higher than 20%?

For what proportion of these corporations was the rate of return negative?

For what proportion of these corporations was the rate of return between 5% and 15%?