Question 388231
Use the normal approximation to the binomial distribution, with {{{mu = np = 450*0.04 = 18}}}, and {{{sigma = sqrt(npq) = sqrt (450*0.04*0.96) = 4.156922}}}.  Then
{{{P(X >= 21.5) = P((X - mu)/sigma = (X - 18)/4.156922 >= (21.5 - 18)/4.156922 = 0.842)}}}.  Hence {{{P(X >= 21.5) = P(Z >= 0.842)}}}.  Now just use any standard normal distribution table to find {{{P(Z >= 0.842)}}} and hence the answer you want.