Afinance professor is interested in comparing the annual turnover rates of mineral stocks compared to stock in oil-related companies. (the turnover rate is the value of shares that change hands as a percentage of the value of all shares.) for a random sample of 31 mineral stocks, the mean turnover rate is 34.9 percentage points, and the standard deviation is 6.7 percentage points. for an independent random sample of 26 oil-related stocks, the mean turnover rate is 31.4 percentage points, and the standard deviation is 5.1 percentage points. turnover rates are approximately normally distributed in each of these populations (mineral stocks, the "x" population, and oil-related stocks, the "y" population).