I have $3$ different mathematics textbooks, $2$ different psychology textbooks, and $2$ different chemistry textbooks. In how many ways can I place the $7$ textbooks on a bookshelf, in a row?
7! 5040
7P7 = ––––––– = –––––– = 5040
(7 – 7)! 1
You might question zero in the denominator,
but zero factorial is defined as 1 so it's okay.
.
+1588 
