The probability of a screen being damaged is: P(d)=3/13=0.23 Thus to get the probability that the first 10 sold were undamaged we use the binomial distribution formula: P(x)=n!/((n-x)!x!)p^x(1-p)^(n-x) from the question: n=13, x=10, p=0.23 hence P(x)=13!/((13-10)!10!)*0.23^(13-10)*(1-0.23)^(10) simplifying the above we get: P(x)=0.255