The duration of a bood at interest rate i is defined as the ratio of t,Ct of to tC1, , where C1 represests the net cash flow from the eccapons and the matanty value of the tond at time t. You are given a 20-year 1,000 par value boed with 4% annal coupons and a maturisy value of 1,000 . Calculate the duration of this bond at 5% inierest