Question 935769
in how many way can 10 letter be put in 10 addressed Envelope such that exactly 5
letter go in wrong envelopes.
<pre>
We can choose the 5 letters to be placed in the correct envelopes C(10,5)
ways and for each of those ways, there are !5 (5 sub-factorial) ways to
place the other 5 wrong.

Answer: C(10,5)*!5 = {{{expr(10*9*8*7*6/(5*4*3*2*1))*expr(Int(5!/e)) = 11080}}}, where Int() is the greatest integer function.

Edwin</pre>