How to do a weighted median?

Is there any way to do a weighted median in Excel?

Consider this example:

Project.....Duration.....Units
---------------------------
a.............10.............3.....
b.............20.............2.....
c.............30.............5.....

I'm trying to get a median of duration, not based on project, but weighted by units.

If I do a =MEDIAN(duration column), that will give me median by project. To get the more accurate number, I need to explode out the above chart to look like this:

Project.....Duration
------------------
a.............10.......
a.............10.......
a.............10.......
b.............20.......
b.............20.......
c.............30.......
c.............30.......
c.............30.......
c.............30.......
c.............30.......

Now if I do =MEDIAN(duration column) it will be weighted by units.

The big question is though, is there a way in Excel to do the calculation on the first table, without exploding it into the second table?

Thanks!