1. 

   Srijana Raghunath Member

   
   How is the simplification done and where are those (n-k)!, n! and K! gone from the denominator?

    

   Srijana Raghunath, Apr 13, 2020

   #1
2. 

   KaustavSen Member

   I think they have forgotten to include the factorial terms in the third step above. Here are my workings including the factorial terms. It leads to the same final answer
   
   

    

   KaustavSen, Apr 14, 2020

   #2
3. 

   Srijana Raghunath Member

   Thank you Kaustav.

    

   Srijana Raghunath, Apr 14, 2020

   #3

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