How do i calculate a progress completion percentage?

I have a total value of 81.



I then have 3 progress values of 20, 10 and 2.



I would like to calculate the completion percentage of these numbers compared to the total. How can I do it?How do i calculate a progress completion percentage?
A.)

If x + y + z = 81



let a = 20 for x; b = 10 for y; c = 2 for z



then (20/x) + (10/y) + (2/z) = 81



therefore: % of Completion = (((20/x) + (10/y) + (2/z))/81)*100



B.)

If x + y + z = 81



let x = 20; y = 10; z = 2



therefore: % of Completion = (((x) + (y) + (z))/81)*100

= (((20) + (10) + (2))/81)*100

= ((20 + 10 + 2)/81)*100

= (32/81)*100

= 39.51%