12.3 Introduction to Probability
Probability – the likelihood that an event will occur. Probability of an event occurring must be a
number between 0 and 1. (many times written as a percent 0% to 100%)
Formula: Probability event A will occur:
P( A) =
There are two types of probability: Theoretical & Experimental
•
Theoretical Probability: When all outcomes are equally likely, the theoretical probability that an event A
will occur is:
•
P( A) =
Experimental Probability: Obtained by performing an experiment, such as conducting a survey, or
looking at the history of the event.
Example 1: A spinner has 8 equal-size sections numbered from 1 to 8. Find the probability of:
a.) spinning a 6.
b.) spinning an odd number.
c.) spinning a number greater than 5.
d.) spinning a 9.
Example 2: A card is drawn from a deck of 52-cards, find each probability.
a.)
drawing the Queen of Diamonds
b.) drawing a heart.
c.) drawing a face card (kings, queens, or jacks)
d.) drawing a card that is not an Ace.
e.) drawing a red face card.
Example 3: You new MP3 Player only has 8 songs stored so far. You set the player to play the songs
at random. The player plays all 8 songs without repeating any song.
a.)
What is the probability that the songs are played in the same order they are listed on
the play list?
b.)
You have 4 favorite songs on the player. What is the p probability that 2 of your
favorite songs are played first, in any order?
Example 4: There are 9 students on the HI-Q team. You draw their numbers one by one to determine
the order in which they answer questions at a HI-Q meet. What is the probability that 3 of the 5
seniors on the team will be chosen last in any order.
Example 5: In 1998 a survey asked Internet users
for their ages. The results are shown in the bar
graph. Find the experimental probability that a
randomly selected Internet user is
a.)
At most 20 years old.
b.)
At least 41 years old.
Homework: Pg 719 – 721 # 12-29all, 41