A pension fund has an average duration of its liabilities equal to 15 years. The fund is considering 5-year maturity zero-coupon bonds and 5 percent yield perpetuities to immunize its interest rate risk. Assuming there are no other assets funding the plan, what proportion of the portfolio should be allocated to the zero-coupon bonds to immunize the entire portfolio? 31,3% 0 62.5% 37.5% 25.0% 50.0%