I was studying for finals and I came across this question:
Assume that: $|A\cup B|=10, |A|=7$, and $|B|=6$. Determine $|A\cap B|$
How do I approach this question? I mean I know the the union must equal $10$ and $|A| +|B| =13$ but I’m lost after that.. Thank you in advance!
Best Answer
Write $x$ for the part of $A$ that's not in $B$, $y$ for the part of $A$ that is in $B$, and $z$ for the part of $B$ that's not in $A$. Then you are given $x+y+z$, $x+y$, and $y+z$, and you are asked for $y$.