Page 166 - Math Course 1 (Book 2)

Probability of Simple Events

Key Concept There are 6 outcomes in which the two numbers
are identical.

Probability 6
P (two identical numbers) =
36
1
1
Words The probability of an event is a ratio or This means there is or
that compares the number of favorable Answer 6 2 6
outcome to the number of possible 16 % chance of rolling
3
outcomes. two identical numbers.
number of favorable outcomes
Symbols P (event) =
number of possible outcomes

Let’s Begin Your Turn!

Find Probability

Suppose a number cube is rolled. What is the
Find Probability probability of rolling a number that is divisible by 3?

Example A. 1 2

6 or 16 3 %
Suppose a number cube is rolled. What is the 1 1
probability of rolling a 4 or a 5? B. or 33 %
3 3
There are 2 numbers on the number cube that are 1
a 4 or a 5: 4 and 5. C. or 50%
2
There are 6 possible outcomes: 1, 2, 3, 4, 5, and 6. 2 2
D. or 66 %
number of favorable outcomes 3 3
P (4 or 5) =
number of possible outcomes
Answer
2 1
= or
6 3
Suppose that two number cubes are rolled. Find the
probability of rolling two numbers whose sum is 8.
The probability of rolling a 4
Answer 1 1
or a 5 is or 33 %
3 3 A. 1 or about 5.6%
15
Suppose that two number cubes are rolled. Find
the probability of rolling two identical numbers. B. 1 or about 8 1 %
12 3
Make a table showing the sample space when
rolling two number cubes. C. 1 or about 11 1 %
9 9
1 2 3 4 5 6
5
1 (1, 1) (1, 2) (1, 3) (1, 4) (1, 5) (1, 6) or about 13.9%
D.
2 (2, 1) (2, 2) (2, 3) (2, 4) (2, 5) (2, 6) 36
3 (3, 1) (3,2) (3, 3) (3,4) (3, 5) (3, 6)

4 (4, 1) (4, 2) (4, 3) (4, 4) (4, 5) (4, 6) Answer
5 (5, 1) (5, 2) (5, 3) (5, 4) (5, 5) (5, 6)
6 (6, 1) (6, 2) (6, 3) (6, 4) (6, 5) (6, 6)
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