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How do I calculate the r value in nCr given that 5Cr = 10? Thanks!

 Jun 8, 2019
 #1
avatar+101431 
+3

We have that

 

   5!

_________    =  10

(5 - r)! *  r!

 

  5 * 4 * 3 * 2

_____________     =   10              divide through by 10

(5 - r)!  * r!

 

 

4 * 3

________     =  1

(5 - r)! * r!

 

 

4 * 3   =      (5 - r)! * r!

 

4 * 3  =   (5 - 2)!  * 2!     =   (5 - 3)! * 3!

 

4 * 3  =   3!  * 2!      =     2!  * 3!

 

12  =  6 * 2    =  2 *6

 

So  either   r = 2    or  r = 3

 

 

cool cool cool

 Jun 8, 2019

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