Question 1164375
<pre>
Must be a misprint.  They aren't equal:

{{{30("nP5"/5!) = (30*"nP4"*(n-4))/5!}}}

By definition:

{{{"nP5" = n(n-1)(n-2)(n-3)(n-4)(n-5)}}}
{{{"nP4" = n(n-1)(n-2)(n-3)(n-4)}}}

So nP5 just has one more factor, (n-5), than nP4 has,

So nP5 = (n+5)nP4.

The misprint in your book was that the (n-4) on the right should have been (n-5).

Books have typos sometimes.

Edwin</pre>