Question

(A11). Suppose a ball is drawn at random from a box containing three white and three black balls. After a ball is drawn, it is then replaced and another drawn. What is the probability that of the first four balls drawn, exactly two are white?

Answer 1

There probability of picking a white ball is $\frac {3}{6}$ =0.5

There are four balls to be chosen and two should be white

P(X =2)

$P(X=x) ={n\choose x} p^x q^{n-x}$

=${4 \choose 2} 0.5^2*0.5^2$

=0.375