
按题说明,应是计算“排列”.
A43 = 4!/(4-3)!= 24
C43 = 24
c52 = 5!/(5-2)!= 20
c65 = 6!/(6-5)!= 720
A(ab)=a*(a-1)*……*(a-b+1)
C(ab)=A(ab)/((a-b)*(a-b-1)*……*1)

按题说明,应是计算“排列”.
A43 = 4!/(4-3)!= 24
C43 = 24
c52 = 5!/(5-2)!= 20
c65 = 6!/(6-5)!= 720
A(ab)=a*(a-1)*……*(a-b+1)
C(ab)=A(ab)/((a-b)*(a-b-1)*……*1)