NAME ______________________________________________ DATE
12-8 Odds
____________ PERIOD _____
(Pages 646–649)
One way to describe the chance of an event’s occurring is by using odds.
Finding
the Odds
• The odds in favor of an outcome is the ratio of the number of ways the outcome can occur
to the number of ways the outcome cannot occur.
Odds in favor number of successes : number of failures
• The odds against an outcome is the ratio of the number of ways the outcome cannot occur
to the number of ways the outcome can occur.
Odds against number of failures : number of successes
Examples
a. Find the odds of getting a 5 when
you roll an eight-sided number
cube.
b. Find the odds against getting an even
number when you roll an eight-sided
number cube.
There is only 1 successful outcome: 5.
There are 7 failures. The odds are 1:7.
There are 4 failures and 4 successes, so the odds
against are 4:4 or 1:1.
Try These Together
1. Find the odds of rolling a 3 with a
six-sided number cube.
2. Find the odds of rolling an odd
number with a six-sided number cube.
HINT: Find the number of successes divided by the number of failures.
Practice
Find the odds of each outcome if a six-sided number cube is rolled.
3. the number 4 or 5
4. the number 1, 2, or 3
5. a prime number
6. a factor of 12
7. a multiple of 3
8. a number less than 5
9. a number greater than 6
10. not a 6
11. not a 1, 2, 3, 4, 5, or 6
12. a factor of 10
A bag contains 9 red marbles, 2 blue marbles, 3 black marbles and
1 green marble. Find the odds of drawing each outcome.
13. a green marble
14. a red marble
15. a blue marble
16. a black marble
17. not a black marble
18. a green or red marble
19. Technology Adela has noticed that the time of day makes a difference
when she is trying to get connected to the Internet. At 4 P.M., she is able
to get connected right away 8 times out of 10. What are the odds of
getting connected right away at 4 P.M.?
20. Standardized Test Practice What are the odds of getting a head when
you toss a penny?
A 1:2
B 2:1
C 0:1
D 1:1
7. 1:2
8. 2:1
9. 0:6
10. 5:1
11. 0:6
12. 1:1
13. 1:14 14. 3:2
Glencoe/McGraw-Hill
105
Answers: 1. 1:5 2. 1:1 3. 1:2 4. 1:1 5. 1:1 6. 5:1
15. 2:13 16. 1:4 17. 4:1 18. 2:1 19. 4:1 20. D
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Glencoe Pre-Algebra