Area under a curve?? (Resolved)

[Foxer]

If I have a distribution of figures :-

Service calls response times

1 hour = 3
2 hours = 5
3 hours = 8
4 hours = 6
5 hours = 4

I need to determine how long it takes to resolve 80% of the service calls.

The figures form a rough bell-curve and from my fading memory of school statistics, is this a question of finding the area under a curve? That is, to define 80% of the area under the graph and the x intercept at that point is my final answer? I guess I'd need to find 80% of the area under the graph starting at the point where x=0.

Or, I could be totally off track.

Any help would be good.

I'm using MS Excel 2003 but can use VBA/code if required.

Thx.