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21C5+21C15=? 

express in simple combinations

1 year ago

Answered By Emily D

21C5 can also be written as  $\frac{21!}{5!\left(21-5\right)!}$21!5!(215)! , which simplifies to  $\frac{21!}{5!15!}$21!5!15!  

 

21C15 can also be written as    $\frac{21!}{15!\left(21-15\right)!}$21!15!(2115)! , which simplifies to  $\frac{21!}{15!5!}$21!15!5!