$7)$ The yearly rate of return on stock indexes is approximately normal. Between $1950$ and $2000$ U$.$S$.$

common stocks had a mean yearly return of about $13\%$ with a standard deviation of about $17\%.$

a$.$ In what range to the middle $95\%$ of all yearly returns lie?

b$.$ In what percent of years does the index gain $30\%$ or less?

c$.$ In what percent of years does the index gain more than $64\%?$