✔ 最佳答案
the probability of x successes in n trials, when the probability of one success is p
= (nCx) (p^x) [(1-p)^(n-x)]
the probability of (n-x) successes in n trials when the probability of oned success is (1-p)
= [nC(n-x)] [(1-p)^(n-x)] {p^[n-(n-x)]}
= (nCx) [(1-p)^(n-x)] p^[x)
=(nCx) (p^x) [(1-p)^(n-x)]
Right?