where are you stuck exactly?
Shares in a collection of companies have an average rate of return (%) of 7, with a standard deviation of 21. Rather than put all my money into one company's shares, I divide it equally between a portfolio of 36 of the companies.
1) What is the expected rate of return on the portfolio?
2) What is the standard deviation of the rate of return of the portfolio?
3) Using a normal distribution, estimate the probability that I will lose money on this portfolio (rate of return 0)