Question

Factor this expression completely and then place the factors in the proper location on the grid. Note:

Answer 1

First we are going to group the terms that contains the common factor $m$ in one parenthesis, and the other ones in another parenthesis:
$mn-4m-5n+20$
$(mn-4m)-(5n+20)$
Notice that our the terms in our first parenthesis have a common factor $m$, and the terms in our second one have the common factor $5$. Lets factor those out:
$m(n-4)-5(n-4)$
Now we have a common factor $(n-4)$ in both terms, so we can factor those out as well:
$(n-4)(m-5)$

We can conclude that the completely factored expression ordered alphabetically is $(m-5)(n-4)$.