19. A pension fund has an average Macaulay duration of its liabilities equal to 15 years. The fund is looking at 4% yield 5 -year maturity zero coupon bonds and 5% perpetuities to immunize its interest rate risk. How much of its portfolio should it allocate to the zero-coupon bonds to immunize if there are no other assets funding the plan? 20. A zero-coupon bond has a time to maturity of 6 years. If the price is $980, what is its modified duration