When I saw a problem on the site, it had a 2.6 rating. Since I really liked the problem, I voted 5 for it, and saw that the rating went from 2.6 to 2.75.

1) How many people voted for it before I did?

2)What would the rating of this problem be if two more people voted 5 for this problem?

The rating of 2.6 simply says that the average of all entries is 2.6. So after you rate a 5, the average has increased to 2.75. By definition, the average is simply the total divided by the number of items, so before you rated the problem,
2.6n = total. Once you rated it, the new total became 2.6n + 5, and the new average can be calculated by dividing the new total by n+1. So

(2.6n + 5)/(n + 1) = 2.75.
Solve this and you get n = 15. You were the sixteenth rater of this problem. If two more people rate a 5,
(2.75*16 + 10)/18 = a new rating of an AVERAGE 3.0

Posted by Jim C on 2003-07-25 04:18:03