An upside down U, which is called the intersection, means the middle. A U, which is called the

union, means everything in the 3 sections. A with line on top means everything but A. B with a

line means everything but B. A includes the middle section and A section. B includes the

middle section and B section. A upside down U B, with a line on top means everything but the

intersection. A U B with a line on top of everything means just the number in the bottom left

corner. A U B line on top of B means everything but the B. A upside down U B line on top of B

means just A. A upside down U B line of top of A means just B. A U B line on top of A means

everything but B.

Example:

40 people went to the park, 25 were playing games with their dogs and 12 were

riding bike and 7 did both. How many did neither?

And the answer is 10 did neither.