Question 155027
Since there are 10 teams, each week there will be 5 games.
It will take 9 weeks to play every other team once. So it takes 18 weeks to play every team twice (once home and once away).

5*9*2 = 90 games

Using mathematics for permutations is {{{10!/(10-2)!}}} = {{{10!/8!}}} = {{{10*9}}} = 90

See this video for more info http://collabvsl.wetpaint.com/page/Basic+Probability