*Probability of Multiple Events

Dependent or Independent?

To find the probability of two events occurring together, you have to decide whether one even occurring affects the other event.

*Dependent Events—the outcome of a second event depends on what happens first.

*Independent Events—the first outcome does not affect the second outcome

Dependent or Independent?

1. Roll a number cube. Then spin a spinner.

2. Pick one flash card, then another from a stack of 30 flash cards.

3. Draw one marble from a bag, then replace it and draw another.

4. Draw one marble from a bag, then draw another without replacing.

Probability of A and B

If A and B are independent events, then

Example: At a picnic there are 10 diet drinks and 5 regular drinks. There are also 8 bags of barbecue chips and 12 bags of regular chips. If you grab a drink and bag of chips, what is the probability that you get a diet drink and regular chips?

Mutually Exclusive Events

Two events that cannot happen at the same time are called mutually exclusive.

You roll a standard die. Are these events mutually exclusive?

1. Rolling a 2 and a 32. Rolling an even number and a multiple of 33. Rolling an even number and a prime number

Probability of A or B

If A and B are mutually exclusive events, then

Examples

*A student can take one foreign language each term. About 37% of students take Spanish. About 15% of students take French. What is the probability that a student chosen at random is taking Spanish or French?

Example

Suppose you reach into this dishand select a token. What is theprobability that the token isround or green?