We have a class of 31 students.

Set A is the set of people who ate an Apple at breakfast. Set A contains 20 students.
Set B is the set of people who ate a Banana at breakfast. Set B contains 10 students.
The number of students in {A ∩ B} is 2.

Assign student counts appropriately for this Venn diagram:



# of students in the area of overlap
# of students in the half-moon labeled A
# of students in the half-moon labeled B
# of students in the box but not inside either circle