solution:
p=ncx ,. p^x.Q^{n-x}\\
where p and q are the probabilities of success and failure respectively.\\
in this case p =0.10 and Q=0.90\\
ncx= \frac{n!}{x!(n-x!)}\\
p(exactly one defect in a random sample of 5)\\
=5(0.10)^1(0.90)^4=0.3281\\
p(no. defects in a random sample of 5)\\
=1(0.90)^5=0.5905