## Thinking Mathematically (6th Edition)

Of 10,000 American adults: $M$ is the set of all 315 tattooed Democratic men. $W$ is the set of all 384 tattooed Democratic women. $D$ is the set of all 699 tattooed Democrats. A set of elements in $M$ and $W$ combined is a set of all 315 tattooed Democratic men and all 384 tattooed Democratic women, which means that it's a set of all $315+384=699$ tattooed Democrats. The set of elements in $M$ and $W$ combined is equal to set $D$.