It's a bit involved: you have to take the present value of each of the bond's cash flows, divide each by the total present value of all the cash flows, and then add up all of these individual durations to get the total duration of the bond. (canadianbusiness.com)
To get the total present value of the credit default swap we multiply the probability of each outcome by its present value to give (en.wikipedia.org)
I multiplied this by the percentile gains computed above to get a total present value of adult earnings gain from pre-K. (investinginkids.net)