The formula for single game Rating looks like this:
Single Game Rating = Number of Tries Value * Time Multiplier * Game Status Multiplier
Game Status has the biggest effect on the Game Rating. Any game that was played receives one of the following statuses:
Number of Tries are valued as following - 0-0, 1-30, 2-40, 3-50, 4-100, 5-80, 6-50, 7-10. The first 3 tries receive lower values then try 4, because it's more of the luck issue then of the actual skill to guess the number in less then 4 tries. After 4th try, values are decreasing because with each new try player has more information.
Time Multiplier. The more time Player spends guessing the number, the lower rating current game will receive. The scale is this - under 30 sec - 1.5, 31-45 - 1.2, 46-60 - 1, 61-90 - 0.8, 91-120 - 0.5, over 121 seconds - 0.3.
Both - Total Combined and Average ratings are displayed, as both of those need to be considered, as Player can receive very high Average Rating by playing only one "perfect" game and never returning to the site again.