There are 2 leagues. American League and National League.
About 20 percent :)
As of right now(2012), there are 16 National League and 14 American League teams. In 2013, the Astros will be moving to the American League which will make the leagues even at 15/15.
32 football teams NFL
There were nine teams that were in the CFL at the beginning of the leagues formation.
I think there is 30 leagues with over 500 teams.
Two leagues: National and American
How many college basketball teams played in 1939
There are 16 teams in CBA (Chinese Basketball Association).
There are 30 National Hockey League teams in North America, 24 in the United States and 6 in Canada. In 2011 this changed to 23 teams in the United States and 7 in Canada when the Atlanta Thrashers were bought and moved to Winnipeg, Canada, becoming the Winnipeg Jets.