For a letter weighing no more than one ounce, which would be about 1 to 6 pages, one first class stamp is needed. As of July 2009, they are 44 cents each in the US.
One.
Ohio is a state, one stamp.
1 first class stamp
Three. Ohio, Oklahoma, & Oregon.
3 Ohio, Oregon, Oklahoma
One, as long as it is 45 cents and the letter is 1 ounce or lower.
Just one of the right denomination. 44¢
None, email does not require a stamp.
Three: Ohio Oregon Oklahoma (I assume you are talking about states in the US.)
One first class stamp is all that's needed.
All you need is ONE first class postage stamp. Provided that it's only a letter.
just 1 stamp if its within the correct size and weight limit