8×7×6×5÷( 1×2×3×4)
= 1680÷24
=70
In mathematics, the formulas of superscript and subscript on C represent the number of combinations. The formula is as follows:
The calculation method of permutation and combination is as follows:
The arrangement A(n, m)=n×(n- 1). (n-m+ 1)=n! /(n-m)! (n is subscript and m is superscript, the same below)
Combination C(n, m)=P(n, m)/P(m, m) =n! /m! (n-m)! ;
For example:
A(4,2)=4! /2! =4*3= 12
C(4,2)=4! /(2! *2! )=4*3/(2* 1)=6