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Algebra 1 Notes:
Lesson 2-6, Part 1:Simple Probability
and Odds
Objectives
• Find the Probability and Odds of simple events
• Describe the difference between probability and odds
• Switch between probability and odds
Vocabulary
•Probability
Vocabulary
•Probability
Usually expressed as a fraction – CAN be a decimal or percent.
ALWAYS between 0 and 1
Probability
The probability of an event can be expressed as:
P(a) = outcomes possible of number total
outcomes favorable of number
Example 1
Find the probability of rolling a number greater than 2 on a die.
P(greater than 2) = 6
4
Example 1
Find the probability of rolling a number greater than 2 on a die.
P(greater than 2) =
About 67%
3
2 or
6
4
Example 2
A class contains 6 students with black hair, 8 with brown hair, 4 with blonde hair, and 2 with red hair. Find each probability.
a) P(black) = 20
6
Example 2
A class contains 6 students with black hair, 8 with brown hair, 4 with blonde hair, and 2 with red hair. Find each probability.
a) P(black) = =20
6
10
3
Example 2
A class contains 6 students with black hair, 8 with brown hair, 4 with blonde hair, and 2 with red hair. Find each probability.
a)P(black) = =
b)P(red or brown) =
20
6
10
3
20
10
Example 2
A class contains 6 students with black hair, 8 with brown hair, 4 with blonde hair, and 2 with red hair. Find each probability.
a) P(black) = =
b) P(red or brown) = =
20
6
10
3
20
10
2
1
Example 2
A class contains 6 students with black hair, 8 with brown hair, 4 with blonde hair, and 2 with red hair. Find each probability.
a) P(black) = =
b) P(red or brown) = =
c) P(not blonde) =
20
6
10
3
20
10
2
1
20
16
Example 2
A class contains 6 students with black hair, 8 with brown hair, 4 with blonde hair, and 2 with red hair. Find each probability.
a) P(black) = =
b) P(red or brown) = =
c) P(not blonde) = =
20
6
10
3
20
10
2
1
20
16
5
4
Example 2
A class contains 6 students with black hair, 8 with brown hair, 4 with blonde hair, and 2 with red hair. Find each probability.
d) P(green) =
Example 2
A class contains 6 students with black hair, 8 with brown hair, 4 with blonde hair, and 2 with red hair. Find each probability.
d) P(green) = = 0 0 20
Example 2
A class contains 6 students with black hair, 8 with brown hair, 4 with blonde hair, and 2 with red hair. Find each probability.
d) P(green) = = 0
e) P(has hair) =
0 20
Example 2
A class contains 6 students with black hair, 8 with brown hair, 4 with blonde hair, and 2 with red hair. Find each probability.
d) P(green) = = 0
e) P(has hair) = = 1
0 20
2020
Equally Likely
0 ½ 1
impossible equally likely certain
to occur to occur to occur
Vocabulary
•Odds
Odds
Favorable : Unfavorable
Example 3
Find the odds of rolling a number greater than two on a die.
Numbers greater than two: 3, 4, 5, 6
Numbers not greater than two: 1, 2
Odds = 4:2
Example 3
Find the odds of rolling a number greater than two on a die.
Numbers greater than two: 3, 4, 5, 6
Numbers not greater than two: 1, 2
Odds = 4:2 or 2:1
Example 4
A card is selected from a standard deck of 52 cards. What are the odds against selecting a 2 or 3?
Not a 2 or 3:
Example 4
A card is selected from a standard deck of 52 cards. What are the odds against selecting a 2 or 3?
Not a 2 or 3: 44
2 or 3:
Example 4
A card is selected from a standard deck of 52 cards. What are the odds against selecting a 2 or 3?
Not a 2 or 3: 44
2 or 3: 8
Odds = 44:8
Example 4
A card is selected from a standard deck of 52 cards. What are the odds against selecting a 2 or 3?
Not a 2 or 3: 44
2 or 3: 8
Odds = 44:8 or 11:2
Switch between probability and odds
1)
Switch between probability and odds
1) 3 :
Switch between probability and odds
1) 3 : 1
2) 5 : 3
Switch between probability and odds
1) 3 : 1
2) 5 : 3 ⅝
Homework
Pgs. 99: 14-56 Evens
