Just .. lol hehe xD
Take (4*5) + (2*1) + (if you have 3 "2" ratings= 3*2, etc.)/ (4+2+3) <- the total amount of ppl who have rated

Then you'll get an avarage of say 4,3 or w.e it is(didn't check). Then you just round up(which in this case will round down to 4).
Get it?

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