1. Section 13.1
Counting

2. Counting the number of elements in a set n(A)
If A { students in class}
n(A) =

3. Those in Set A that are not in Set B = 35 – 18 = 17
Think those 18 in both count for both A and B so they must be taken out of each.
Lets look at a picture of this (Venn diagram)
Those in Set A that are not in Set B = 35 – 18 = 17
Those in Set B that are not in Set A = 52 – 18 = 34
So total is = 69 students.

5. This is the formula we just used.
Does this remind you of anything?

9. U
A B 7 4 9 C
How many are in A? How many are in B?
How many are in B and C? How many are in A but not C?
How many are in A and C but not B? How many in B or A?

10. This is a counting problem with choices at each level
This is a counting problem with choices at each level. A Venn diagram is not appropriate in this case but there is no overlapping just different paths.
Instead we will use a stem diagram.