Ooooooops hmm how do I explain ?? hehe ... try to take a simple example let us suppose the word in LAMA and we need to make 2 letter words from that. OKAY ??

 

So let us see ... by using the previous approach

 

We will find coefficeint of x² in the expression

    2! (1 + x)²(1 + x + x²/2)

   

    So we find coefficeint of x² in ( 1 + x² + 2.x).(1 + x + x²/2)

 

    The terms corresponding to x² are 2! ( 1 + 2.1 + 1/2)x²

    which is 7.

 

     Now see the normal way the two letter words can be 

AA, AL, AM, LA, LM, MA, ML

 

which are 7 in number so the approach works okay??

 

The expression will change if u make 5 letter words .. in this case u will replace 4! by 5! and find coefficiet of x^5.

 

okay ... cheers