$144$
In a group of $320$ people, only $10$ are millionaires but $4$ of the $170$ college graduates are millionaires. How many non-college graduates are not millionaires?
$144$
Let $\Omega$ denote the set of all $320$ people. Let $C$ and $M$denote the set of people that went to college and the set of millionaires,respectively. We have $|\Omega|=320$, $|C|=170$, $|M|=10$, and $|C\cap M|=4$.
We note that $M'\cap C'$ denotes the set of non-college graduates who are not millionaires.Now,\[\begin{align}|M'\cap C'|&=|(M\cup C)'|\\
&=|\Omega|-|(M\cup C)|\\
&=|\Omega|-(|M|+|C|-|M\cap C|)\\
&=320-(10+170-4)\\
&=320-176\\
&=144.\end{align}\]Therefore, $144$ non-college graduates are not millionaires.