ROI 跟時間不答上。

Internal Rate of Return, 能和時間拉上關係。讓我把這題目改一下：

Today, I can buy the stock for $100 and one year from now I will get $20 dividend;  however, two years from now I might have to sell the stock at $90, what is the IRR?

這些時間是需要的，因爲我們要discount the cash flow.

100 = 20 / (1+x) + 90/(1+x)^2

大概5%？