The Price of a 20 year zero coupon bond is P = (1+i)^(-20). if (1+i) rises by 1% the prices falls by 20%. which is the bond duration. A 4.5% coupon bond has a lower duration as its duration is a weighted average of the duration of the principal and the duration of all of the coupons (which have durations from 6 moths to 20 years. The coupon bond will be less price sensitive.
