This is borderline just a math question but here goes

Lets say we have an estimated number of days something takes, the actual number of days it ended up taking, and a % that when you divide the two it gives you an idea of the performance.

Lets say there are several of these that add up to a total % which gives the performance of the total factory or whatever:

So:

NAME Completion % Estimated Days Days it actually took
A 100% 5 5
B 50% 2 4
C 53% 34 64
D 71% 17 24
E 46% 3 6.5
F 72% 13 18
TOTAL 61% 74 121.5

So you can see in order to see who really drove the total 61% you have to try to look at who had the most days and try to guess at it.

My question: is there some kind of weighted average formula or some other method that will allow me to more easily quantify the major drivers of the low 61% total?

Thanks!