Use the cash flows of a portfolio of the following three bonds to calculate the yield to maturity of he porfolio. Each bond has a face value of $1,000. Use the cash flows and yield to maturity to calculate the duration of the portfolio:

Three-yeear zero coupon bond with 5% yield.

Five-year zero-coupon bond with 7% yield.

Seven-year zero-coupon bond with 6% yield.

Verify your portfolio duration calculation using the weighted average of the individual bond durations.