题目有点多啊，大家耐心一点耐心一点~
On January 1, a risk manager observes that the 1-year continuously compounded interest rate is 5% and storage costs of a commodity product A is USD 0.05 per quarter (payable at each quarter end). He further observes the following forward prices for product A:
March               5.35
June                 5.90
September       5.30
December        5.22
Question: What is the annualized rate of return earned on a cash-and-carry trade entered into in March and closed out in June?
答案是这样的  5.9=5.35e^(r*0.25)+0.05  算出r就可以了。可是为什么不先把0.05按0.05的无风险利率和0.25year折现到今天，这个值是0.0494，再用5.9=(5.35+0.0494)e^(r*0.25)呢，不是有个公式是F=(S+U)e^(rT)吗？这里面U就是storage cost的折现值啊，按照正确答案那种思路，其实相当于0.05是按照r和0.25year折现到今天，为什么是用r不是用无风险利率呢？