Let P be the prob. that an MP3 player produced in a certain factory is defective, with p assumed a priori to have the uniform distribution on 0 to 1. in a sample of one hundred MP3 players, 1 is found to be defective. based on this experience, determine the posterior expected value of P.

the solution says the posterior prob. distribution of p is beta with parameters 1+1=2 and 99+1=100. i don't understand why this is beta distribution?thx.