Let Bfi=1,2,3 be three independent events in a sample space. The probability that only B1 occur is α,only  B2occurs is β and only B3occurs is γ. Let p be the probability that none of the eventsBf  occurs and these 4 probabilities satisfy the equations  α−2βp=αβand β−3γp=−2βγ (All the probabilities are assumed to lie in the interval (0, 1). Then  PB1PB3is equal to  _________.