Probabilities from Venn Diagrams Flashcards

All 3 cards in this deck

What are the steps to find a probability from a completed Venn diagram?

e.g. $A$ only $3$, both $2$, $B$ only $4$, outside $1$; find $P(A\cap B)$

1. Count the elements in the region asked for: $2$
2. Count all the elements in $\xi$: $3+2+4+1=10$
3. Write region $\div$ total: $\frac{2}{10}$

True or false? To find how many elements are in $A \cup B$, add the number in $A$ to the number in $B$.

False. That counts the elements in the intersection twice.

True or false? Elements written outside both circles are left out of the denominator when a number is chosen at random from $\xi$.

False. They are part of the universal set, so they count in the total.