chess.com forgot their abacus

   I'm in a group tournament for the amateur astronomers and I can't figure something out. There are nine players playing two games against everyone else in the tourney so the display shows a total of 144 spots to record the outcomes. So fairly simple to figure 72 unrepeated games are in the display. #1 player has 16 #2 player would then have 14 (because 2 were shown in the first players line) #3 player 12 etc.. Added all up ... 72 games. Now, 9 games are completed and the page says that the tournament is 20% completed. Isn't 9 out of 72 12.5%? where did I go wrong? Any help would be appreciated.  

Is there a second round where fewer players would be involved ?  If not , your calcs seem correct.  What's the tourney called (or give its url)

I concur with diomed1 and mxdplay4 http://www.chess.com/tournament/amateur-astronomers. And maybe it's dodgy maths that causes my rating to keep falling!

I concur with the OP, 9/72<20%

   No second round mxdplay4, and thanks artfizz and dwaxe I didn't think my math skills had degraded that much

Maybe it's rounding up to the nearest 10%?

Baseballfan wrote: Maybe it's rounding up to the nearest 10%?

It calculates these other single-round tournaments correctly:

I had a look at some others and quickly found another one 7% out (89% v 82%). It isnt rounded up to next 10%, maybe there is a delay in the result going up even though the stats computer knows a result ?

I'm wondering whether whoever wrote the algorithm to work out the completed %age forgot to take out the XX s from the cross table.  There are 18 of these in a 9 man tourney with 72 games and 18 / (72+18) = 0.2.  (20%)

It needs one of the programmers to provide an answer.

Here is another theory.

Currently 9 of 72 complete with 35 in progress.

Current incorrect calculation: 9/(9+35) * 100 = 20.4% => 20%

Games neither completed nor in progress not included.

Edit:

Currently 10 of 72 complete with 35 in progress.

Current incorrect calculation: 10/(10+35) * 100 = 22.2% => 22%

    mxdplay4, then the % would stay the same throughout the tourney because none of those factors would change.(total # games, double Xs, etc)           Taddude, you might have it, they're figuring using the wrong numbers or they shouldn't say " _____% of the tournament is complete". Thanks for all the help

Alright, maybe it's cuz I'm a blond, but I'm still confused.  In the following tournament, we have 12 players playing against each other with no 2nd round (which is what I thought the culprit was all along, but I guess not). 

12 players x 11 opponents each = 132 games.

At the moment there are 56 completed games, and 76 games still in progress. (56+76=132 - no problem here)

It claims that the tournament is 56% complete.  Fewer than half the games have been completed and yet it says that the tournament is over half done.  By my calculations, 56 would be 56% of 100 games, not 132.  66 games complete would be the 50% mark.  56/132 = 42%.  Where does the number 56% come from?

http://www.chess.com/tournament/cti---introductions

Same thing in this tournament:

http://www.chess.com/tournament/paul-newman-memorial 

9 players x 8 opponents = 72 games.  10 complete, 62 remaining.  10/72 = 14% and yet it claims that the tournament is 22% complete.  I thought computers were supposed to be good with math.  How are they arriving at these numbers?

ok. i'll investigate. computers are only as smart as the people who program them and... doh!

As the fireman said ' No one is inflammable'.

Im pretty sure this is a mathematical error on peoples part. If there are 9 people in the tourny that means there is actually 9+8+7+6+5+4+3+2+1 = 45 games. (that is if everyone plays everyone once) And if there are 10 complete games then 10/45 = 2/9 which is approx. 22%.

Put in down on paper. 9 names then draw a line from each player to the other names. When you get to the second player you dont join this back to the first player as he is already playing him in a game so therefore the second guy has 8 games and the 3rd guy has 7 games and so forth. Dont think this is the best explanation ever but should get my point accross all the same.

This is correct and based upon  a sum of the digits calculation, which can also be expressed as (X*(X+1))/2

in this tournament: http://www.chess.com/tournament/cti---introductions

there are [11+10+9+8+7+6+5+4+3+2+1]*2 = 132 games.

something is clearly wrong.

:completed games+won "currently ongoing games"/#games =%complete 

Skeptikill, Nice theory, except that in tournaments, everybody plays everybody else in TWO games (once as white and once as black).  There's no need to write it down on paper as the pairings are displayed on the tournament homepage.  If there are 9 players, each player has 8 opponents, 2 games each, that's 16 games per player.  As you said, you can't multiply 9 x 16 cuz you would be counting each game twice.  So you cut the number in half for accuracy, and 9 x 8 = 72 games in the tournament.

Perhaps the problem with %'s only arises when players have to play each other more than once.

   I believe TadDude has the correct answer (see above). Just take "games in progress" to mean games with at least one move made not all remaining games to be played in the tournament.