how'd you know?

a brunette and a blonde were sitting together eating lunch and the brunette thought of a little trick.she asked the blonde to think of a number between 4 and 6.the blonde thought to herself for a few seconds and said"ok  i got it." the brunette said she was physcic and was going to guess the number.the blonde said"you'll never guess my number" the brunnete then smiled and asked"is your number...5?" the blonde was shocked and asked "o.m.g how did you know?!?" then the brunette was shocked and the blonde asked again "how'd you know?" the brunette just burst out laughing