# Math Help - Intersection and Union problem

1. ## Intersection and Union problem

How do I do this? Freshman in need of serious help

A={3,6,7,12} B={1,3,5,7,15} C={6,7,11,15}
(A"union"B)"intersection"C

2. ## Answer my question

People please answer. I don't have the symbol for union and intersection on my laptop. That's why I put the words in parenthesis.

3. $A \cup B = \{1,3,5,6,7,12,15 \}$

$(A \cup B) \cap C = \{6,7,15 \}$

4. Originally Posted by tukeywilliams
$A \cup B = \{1,3,5,6,7,12,15 \}$

$(A \cup B) \cap C = \{6,7,15 \}$
Ok why did you get rid of the eleven. can you explain (so I can explain it in class)?

5. There's no $11$ in $A \cup B$ but there is an $11$ in $C$. So $A \cup B$ and $C$ do not share $11$ as a common element (i.e. the intersection between these two sets does not contain $11$).

6. ## Replying to your good answers

Originally Posted by tukeywilliams
There's no $11$ in $A \cup B$ but there is an $11$ in $C$. So $A \cup B$ and $C$ do not share $11$ as a common element (i.e. the intersection between these two sets does not contain $11$).
Oh, I see. You only keep common numbers/elements. Sorry for seeming like a noob. My teacher didn't teach us this.

7. yes that is correct.