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Suppose that there are many stocks in the security market and that the characteristics of stocks A and B are given as follows: Stock Expected Return Standard Deviation A 10% 5% B 15 10 Correlation =-1 Suppose that it is possible to borrow at the risk-free rate, r f . What must be the value of the risk free rate? ( Hint: Think about constructing a risk-free portfolio from stocks A and B. )