6th Grade Math Textbook, Progress

Update your skills. See page 15.

Probability

8-13

Probability is a measure of the likelihood of an event.

The probability of an event is any number from 0 to 1.

A probability of 0 means an event is impossible.

A probability of 1 means an event is certain to occur.

P(E) 


number of favorable outcomes

total number of possible outcomes

When you use a formula to find probability you are finding theoretical probability.

Theoretical probability can be

defined by the formula:

Each number on the spinner is one possible outcome, or

result of spinning the spinner. The sample space or the

set of all possible outcomes is {1, 3, 5, 7, 9}.

Use the spinner to find each theoretical probability.

P(2) 
^05 
 0

impossible

P(odd number) 
^55 
 1

certain

P(7) 
^15 
0.2

possible

19

3

5

7

Complementary Events

Two events, E and notE, are

complementary if both events cannot

occur at the same time. The sum of

their likelihood of occurring is 1.

P(not 7) 
 1 P(7)


 1 

1

5 


 
0.8

4

5

Mutually Exclusive Events

Two events, A and B, that have no

outcomes in common, are called

mutually exclusive, or disjoint events.

P( 5 or  7 ) 
P( 5 ) P( 7 )




2

5 

1

5 



0.6

3

5

1

certain

0

impossible

1

2 = 0.5

Unlikely Likely

possible between 0 and 1

P(E) P(not E) 
 1 P(A or B) 
P(A) P(B)

3.3

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