The standard deviation of the market-index portfolio is 20%. Stock A has a beta of 1.5 and a residual standard deviation of 30%.

a. What would make a larger increase in the stock's variance: an increase of .15 in its beta or an increase of 3% (from 30% to 33%) in its residual standard deviation?

b. An investor who currenty holds the market-index portfolio decides to reduce the portfolio allocation to the market index to 90% and to invest 10% in stock A. Which of the changes in (a) will have a greater impact on the portfolio's standard deviation.