Problem 3061. Mirror, mirror on the wall, who is fairest of them all?

The Elo rating system was featured in the movie The Social Network during the algorithm scene where Mark Zuckerberg released Facemash.

In the scene Eduardo Saverin writes mathematical formulas for the Elo rating system on Zuckerberg's dorm room window. The Elo system is employed to rank coeds by their attractiveness. The equations driving the algorithm are shown briefly (Ea and Eb).

You should know these equations now (See problem 3056) :

Ea is the expected probability that Girl A will win the match against Girl B.

Ra is the rating of Girl A, which changes after tournament, according to the formula (Ra )n = (Ra )n-1 + 32 (W - Ea ) where W = {1,0.5,0}.

Now imagine a single round-robin tournament where each girl plays (is compared with) every other girl once. A judge (me for the problem) gives a note :

  • 1 if girl A is more attractive than girl B
  • 0 if girl B is more attractive than girl A
  • 0.5 if same attractiveness

I give you the tournament results (2 on the main diagonal).

Find the final rating of Snow White (she is unique).

Consider that all girl begin the tournament with a rating of 1000.

You can observe that the total number of attractiveness (ELO) points remains constant.

Solution Stats

81.82% Correct | 18.18% Incorrect
Last solution submitted on May 07, 2019

Problem Comments