5论坛币问一道有关金融CAPM的题目

The current price of a share of stock in the XYZ company in Italy is 2 Euro and its expected yield over the year is 15%. The market risk premium in Italy is 10% and the risk-free interest rate is 5%. What would happen to the stocks' curent price if its expected future payout remains constant while the covariance of its rate of return with the market portfolio falls by 50%?
可以算出最后XYZ company的股票具体价格吗？？为啥我觉得缺条件算出价格呢~~求高手指点！求详细公式和过程~谢谢~~

cost of equity=risk-free+beta*risk premium;
15=5+beta*10, beta=1.
beta=cov(equity, market)/var(market).
所以cov(equity, market)变成原来的一半的时候，beta变成原来的一半也就是0.5.
用新的beta重算cost of equity=5+0.5*10=10.
用DDM，把股票看成永续年金，P=k/g. g从原来的15变成了10， 股价也要相应的乘上10/15。

β=r*σi/σm, 当股票与市场的系数下降50%，β也降低50%。权益成本=β*0.1+0.05=x。股利是2*0.15=0.3，根据永久股利模型，权益成本为0.15.调整后的权益成本是0.1，股价为3元。仅供参考，呵呵