b 的maturity呢？
还有题目有点看不懂
1， the duration of a zero coupon band= its maturity
2,holding maturity constant, a bond's duration is lower when the coupon rate is higher
3,,holding  coupon rate constant, a bond's duration increases with its time to maturity
4,,,holding other factors constant, a bond's duration is higher  when the bond's yield to maturity  rate is lower
5,,,,the duration of a level perpetuity is (1+y)/y
不知道以上规则能不能帮您解决这个问题