A Chess Championship was held in Norway, in which 4 players namely Magnus, Tal, Garry, and Anand participated. Since Tal had not participated in official chess for a while, he was assigned the rating of 0. Others were assigned the ratings 200, 400, and 600 in no order.
Each player played every other player once, and a player played only 1 game in a day. The tournament lasted for 3 days. At the end of the tournament, the person who won the most number of matches was declared the winner.
With each match, the assigned ratings of players change as follows:
If Players 1 and 2 with ratings X and Y respectively are playing where X>Y, then $$a=\frac{\left(X-Y\right)}{4}$$. If Player 1 loses, then the ratings would become (X-a, Y+a). If Player 1 wins, the ratings become (X+a, Y-a). During the tournament, the value of a was always a natural number.
The ratings were updated at the end of each match.
The arbiter noted the following things at the end of the tournament:
1. The ratings of all the Players after both Day 1 and Day 2 were multiples of 10.
2. All the games in the tournament were 'upsets' that is, a lower-rated player won against a higher-rated player in each game.
3. No match was a tie in the tournament.