SOLUTION: nC12 = nC8, find n, then find the value of nC17

If you know that , then
it's easy.

r = 12,  n-r = 8
        n-12 = 8
           n = 20

Otherwise:



Cross-multiply:



Divide both sides by n!



Write 12! as 12∙11∙10∙9∙8!



Divide both sides by 8!



Write (n-8)! as (n-8)∙(n-9)∙(n-10)∙(n-11)∙(n-12)!



Divide both sides by (n-12)!



n-8=12, n-9=11, n-10=10, n-11=9
  n=20,   n=20,    n=20,    n=20

Answers: ,  

Edwin