Download An Introduction To Probability

An Introduction To
Probability
Algebra 2
Definitions:
Probability: the likelihood that an event
will occur. Has to be a number between 0
and 1.
 An event that is certain to occur has a
probability of 1
 An event that cannot occur has a
probability of 0
 An event that is equal likely and unlikely
has a probability of ½ .

The Theoretical Probability Of An
Event

When all outcomes are equally likely the
theoretical probability that an even A will occur
is…
number of outcomes in A
P( A) 
Total number of outcomes

Theoretical Probability is often just called
probability
Probability

Probability can be expressed as either a
fraction, decimal, or percent.
Example:

A spinner has 8 equal-size sectors
numbered from 1 to 8. Find the probability
of
 Spinning
a 6.
 Spinning a number greater than 5.
Example:

There are 9 students on the math team.
You draw their names one by one to
determine the order in which they answer
questions at a math meet. What is the
probability that 3 of the five seniors on the
team will be chosen last, in any order.
Example:

Five cards are drawn from a standard 52card deck. What is the probability that the
first 2 cards are red.
Experimental Probability

Experimental Probability: A calculation of
the probability of an event based on
performing an experiment, conducting a
survey, or looking at the history of an
event.
Example:

Ninth graders must enroll in one math
class. The enrollments of ninth grade
student the previous year are shown in the
bar graph. Find the probability that a
randomly chosen student from this year’s
ninth grade class is enrolled in
 Consumer
Math
 Algebra 1 or Introduction to Algebra
Example:

You made 15 of 21 free throw attempts.
Find the probability that you will make you
next free throw.
Geometric Probabilities

Geometric Probability: probabilities found
by calculating a ratio of two lengths, areas,
or volumes
Example:

Find the probability that a randomly thrown
dart would hit the shaded portion of the
target.
Example:

A store is open from 8am to 8pm. The
manager works from 9am to 4pm. What is
the probability that the manager is there
during the same time as a customer who
arrives randomly during the store’s hours
of operation and stays for 15 minutes?
Example:

The target for a bean bag toss game is a
rectangle 3 feet wide and 4 feet with 3
circular holes each with a radius of 1 foot.
What is he probability that a bean bag
thrown randomly at the target will pass
through one of the holes.