１０００＊＊＊ - 経済統計練習帳

def bi(n,k,p1):
 
    c1=1
    for i in range(n):
       c1=c1*(i+1)
 
    c2=1
    for i in range(k):
        c2=c2*(i+1)
 
    c3=1
    for i in range(n-k):
        c3=c3*(i+1)
 
    b1=c1/(c2*c3)
 
    b2=(1-p1)**(n-k)
    b2=b2*p1**k
 
    return b1*b2
 
ans = bi(8,3,0.75)
print(ans)