You are given a portfolio consisting of two bonds:
• 60% of the portfolio is invested in a two-year coupon bond, for which a unit of it has an annual coupon of 15%, with par and redemption value of $100, currently selling for $93.50
and
• 40% of the portfolio is invested in a zero-coupon bond for which a unit of it will pay $100 in four years exactly, with a price of such a unit today of $49.51.
Find the duration of this portfolio.