Trivia Question

Lexi is working on a logging presentation at school, so yesterday she had four girls, who are in her group, come over to work on the project.  She comes up to ask me "What year did Washington become a state?"  I say, "I have no idea." She looks at me funny and then says mockingly, "you really don't know?"  Like I'm some sort of idiot.  So tell me do you know?