问题如下：
A bond portfolio consists of the following three fixed-rate bonds. Assume annual coupon payments and no accrued interest on the bonds. Prices are per 100 of par value.
The bond portfolio’s modified duration is closest to:
选项：
A.7.62.
B.8.08.
C.8.20.
解释：
A is correct.
The portfolio’s modified duration is closest to 7.62.Portfolio duration is commonly estimated as the market-value-weighted average of the yield durations of the individual bonds that compose the portfolio.
The total market value of the bond portfolio is 170,000 + 120,000 + 100,000 = 390,000.
The portfolio duration is 5.42 × (170,000/390,000) + 8.44 × (120,000/390,000) + 10.38 × (100,000/390,000) = 7.62.
为什么用Market Value, 而不用Price？
什么情况下，A和B的Market Value 比 Price 大了那么多？
