Combinatorics

Factorial Expressions

Computing n!/(n-k)!

  • High school
  • about 3 min
  • 2 of 11 in the family
Not started

Numerator: 7!

7654321

Denominator: 4!

4321
=7×6×5= 210
7!(7−3)!=7!4!=7×6×5=210\frac{7!}{(7-3)!} = \frac{7!}{4!} = 7\times6\times5 = 210

Gray numbers cancel with denominator. Only blue remain: 7 × 6 × 5 = 210.

Where it is taught