What is Probability?

Probability:

​The likelihood of something happening or being the case.

How is Probability Written?

​Probability is written as a decimal, percent or fraction.

• ​Ex: 0.87 = 87%

• Ex: 2/5 = 0.4

• 30% = 3/10​

• ​Probability can only range from 0-1.

• A probability of 1 means the event is CERTAIN to happen.

• What does a probability of 0 mean?

​How do we find probability?

​

• Probability = # of desired outcomes / total # of outcomes

• P(girls) = (# of girls)/(total # of students)

Probability Examples

​A bag of marbles has 22 marbles in it: 6 red, 11 blue, and 5 yellow.

​

Calculate the following probabilities of randomly selecting a marble.

P(red)

P(blue)

P(yellow)​

Probability Examples

​A bag of marbles has 22 marbles in it: 6 red, 11 blue, and 5 yellow.

​

Calculate the following probabilities of randomly selecting a marble.

P(red or blue)

P(blue or yellow)

P(green)

Probability Examples

You randomly select a card from a normal deck of cards: 52 cards, 4 suits, Ace-King.

Calculate the following probabilities of:

​

P(diamond)

P(King)

P(5 of hearts)