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?

(Part a)

Let the total number of members who had voted prior to the individual's vote be d.

By the problem:
2.6*d + 5 = 2.75(d+1)
Or, 0.15*d = 2.25
Or, d = 15

Accordingly, precisely 15 members voted for the problem prior to the individual.

(Part b)

Two more members voted 5 each, so that a total of three new members (including the individual) has each voted 5 each. Since 15 members had already voted 2.6 each for the problem, it follows that the new rating would be:

(2.6*15 + 3*5)/18 = 3 

Edited on November 14, 2007, 4:28 am

Posted by K Sengupta on 2007-11-14 04:03:36