Appraisal CAlculation(FORMULA)

hello,
i have a query!!!!
say for example if a person (assesse has assesed himself on 5 parameters as: 4, 3, 4, 5, 4 (say x)
Total score: 20
The weights for the parameters are: 4, 3, 3, 4, 2 (say y)
Total weights: 16
Now if we apply the weighted mean method: summation of (X*Y)/summation of y: it is coming to: 65/16= 4%
then how can we rate him as: 70-80%....v good
80-90%........excellent ?
ayona

Can anyone help on below statement?
The scenario is same with me and how to take these value to 100 ratings

Hello All..
I am Prajakta I have basic knowledge appraisal but i want to know how to calculate performance appraisal formula please help me.