## Thinking Mathematically (6th Edition)

$\emptyset$ (there were no years in which more than $55\%$ were pretty happy and $12\%$ were not too happy.)
Let's call: $A$ - The set of years in which more than $55\%$ were pretty happy. $B$ - The set of years in which $12\%$ were not too happy. $C$ - The set of years in which more than $55\%$ were pretty happy and $12\%$ were not too happy. $C=A\cap B$ From the graph we can see that: $A=\{1990, 2000, 2010\}$ $B=\{1980\}$ $C=A\cap B=\emptyset$