Before i begin ..

How many states are there in the U.S.?

There are fifty (50) states and Washington D.C.
The last two states to join the Union were Alaska (49th) and Hawaii (50th). Both joined in 1959.
Washington D.C. is a federal district under the authority of Congress. Local government is run by a mayor and 13 member city council. Washington DC is represented in Congress by an elected, nonvoting Delegate to the House of Representatives and residents have been able to vote in Presidential elections since 1961.
Puerto Rico is a commonwealth associated with the U.S. Its indigenous inhabitants are U.S. citizens. Puerto Ricans are unable to vote in U.S. Presidential elections but they do elect a nonvoting resident commissioner to the U.S. House of Representatives.
Dependent areas: American Samoa, Baker Island, Guam, Howland Island, Jarvis Island, Johnston Atoll, Kingman Reef, Midway Islands, Navassa Island, Northern Mariana Islands, Palmyra Atoll, Puerto Rico, Virgin Islands, Wake Island
note: from 18 July 1947 until 1 October 1994, the US administered the Trust Territory of the Pacific Islands, but recently entered into a new political relationship with all four political units: the Northern Mariana Islands is a commonwealth in political union with the US (effective 3 November 1986); Palau concluded a Compact of Free Association with the US (effective 1 October 1994); the Federated States of Micronesia signed a Compact of Free Association with the US (effective 3 November 1986); the Republic of the Marshall Islands signed a Compact of Free Association with the US (effective 21 October 1986)

Source: The CIA Factbook 2003