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ARE YOU READY FOR THE QUIZ?
1.
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Yes
No
That depends on how you
measure ‘readiness’.
33%
33%
33%
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UPCOMING IN CLASS
Monday HW4
CHAPTER 14
From Randomness to Probability
MODELING PROBABILITY (CONT.)
The probability of an event is the number of
outcomes in the event divided by the total
number of possible outcomes.
P(A) =
# of outcomes in A
# of possible outcomes
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FORMAL PROBABILITY
1.
Two requirements for a probability:
2.
A probability is a number between 0 and 1.
For any event A, 0 ≤ P(A) ≤ 1.
Probability Assignment Rule:
The probability of the set of all possible outcomes
of a trial must be 1.
P(S) = 1 (S represents the set of all possible
outcomes.)
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FORMAL PROBABILITY (CONT.)
3.
Complement Rule:
The set of outcomes that are not in the event A is
called the complement of A, denoted AC.
The probability of an event occurring is 1 minus
the probability that it doesn’t occur: P(A) = 1 –
P(AC)
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FORMAL PROBABILITY (CONT.)
4.
Addition Rule (cont.):
For two disjoint events A and B, the probability
that one or the other occurs is the sum of the
probabilities of the two events.
P(A or B) = P(A) + P(B), provided that A and B are
disjoint.
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FORMAL PROBABILITY
5.
Multiplication Rule (cont.):
For two independent events A and B, the
probability that both A and B occur is the product
of the probabilities of the two events.
P(A and B) = P(A) x P(B), provided that A and B
are independent.
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PROBLEM 5
A consumer organization estimates that over a 1year period 16% of cars will need to be repaired
once, 7% will need repairs twice, and 1% will
require three or more repairs.
Suppose you own two cars.
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WHAT IS THE PROBABILITY THAT NEITHER
CAR WILL NEED REPAIRED THIS YEAR?
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2.
3.
4.
.76
.24
.5776
.0576
25%
25%
25%
25%
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2.
3.
4.
WHAT IS THE PROBABILITY THAT BOTH
CARS WILL NEED REPAIRED THIS YEAR?
1.
2.
3.
4.
.76
.24
.5776
.0576
25%
25%
25%
25%
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2.
3.
4.
WHAT IS THE PROBABILITY THAT AT LEAST
ONE CAR WILL NEED REPAIRED THIS YEAR?
1.
2.
3.
4.
.76
.24
.5776
.4224
25%
25%
25%
25%
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4.
PROBLEM 9
For a certain candy, 10% of the pieces are yellow,
20% are blue, 10% are green, and the rest are
brown.
If you pick a piece at random, calculate the
probability of the following…
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WHAT IS THE PROBABILITY THAT YOU PICK
A BROWN PIECE?
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2.
3.
4.
40%
60%
.4
.6
25%
25%
25%
25%
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4.
WHAT IS THE PROBABILITY THE PIECE YOU
PICK IS YELLOW OR BLUE?
1.
2.
3.
4.
.1
.2
.8
.9
25%
25%
25%
25%
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2.
3.
4.
WHAT IS THE PROBABILITY THE PIECE YOU
PICK IS NOT GREEN?
1.
2.
3.
4.
.1
.2
.8
.9
25%
25%
25%
25%
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2.
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4.
WHAT IS THE PROBABILITY THE PIECE YOU
PICK IS STRIPPED?
1.
2.
3.
4.
0
.1
.5
1
25%
25%
25%
25%
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PROBLEM 9
Now suppose you pick three pieces.
You observe three independent events.
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WHAT IS THE PROBABILITY OF PICKING THREE
BROWN CANDIES?
1.
2.
3.
4.
5.
.064
.4
.64
.936
1.2
20%
20%
20%
20%
20%
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2.
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4.
5.
WHAT IS THE PROBABILITY OF THIRD ONE
BEING THE FIRST RED?
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2.
3.
4.
0.008
0.128
0.2
0.8
25%
25%
25%
25%
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2.
3.
4.
WHAT IS THE PROBABILITY THAT NONE
ARE YELLOW?
0.001
0.729
0.9
0.999
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WHAT IS THE PROBABILITY OF AT LEAST
ONE GREEN CANDY?
0.1
0.271
0.729
0.9
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PROBLEM 11
You roll a fair die three times
Again, each roll is independent of the last.
Sample space of one roll {1,2,3,4,5,6}
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WHAT’S THE PROBABILITY YOU ROLL ALL
5’S?
1.
2.
3.
4.
0.0046
0.1667
0.8333
0.9954
25%
25%
25%
25%
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2.
3.
4.
WHAT’S THE PROBABILITY YOU ROLL ALL
EVEN NUMBERS?
1.
2.
3.
4.
0.125
0.5
0.875
1
25%
25%
25%
25%
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4
WHAT’S THE PROBABILITY THAT NONE ARE
DIVISIBLE BY 2?
1.
2.
3.
4.
0.125
0.5
0.875
1
25%
25%
25%
25%
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4
WHAT’S THE PROBABILITY THAT AT LEAST
ONE IS 3?
1.
2.
3.
4.
0.1667
0.4213
0.5787
0.8333
25%
1.
25%
25%
2.
3.
25%
4.
WHAT’S THE PROBABILITY THAT NOT ALL
ARE 3’S?
1.
2.
3.
4.
0.0046
0.1667
0.8333
0.9954
25%
25%
25%
25%
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2.
3.
4.
PROBLEM 15
On September 11, 2002, a particular state
lottery’s daily number came up 9-1-1. Assume
that no more than one digit is used to represent
the first nine months.
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WHAT IS THE PROBABILITY THAT THE WINNING
THREE NUMBERS MATCH THE DATE ON ANY
GIVEN DAY THAN CAN BE REPRESENTED BY A
THREE DIGIT NUMBER?
25%
25%
25%
1.
2.
3.
4.
25%
0.000
0.001
0.273
1
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2.
3.
4
WHAT’S THE PROBABILITY THAT THE WINNING
THREE NUMBER MATCH THE DATE ON ANY
GIVEN DAY THAT CAN BE REPRESENTED BY A 4DIGIT NUMBER?
25%
25%
25%
25%
1.
2.
3.
4.
0.000
0.001
0.273
1
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WHAT’S THE PROBABILITY THAT A WHOLE YEAR
PASSES WITHOUT THE LOTTERY NUMBER
MATCHING THE DAY?
1.
2.
3.
4.
0.001
0.694
0.761
0.999
25%
25%
25%
25%
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FOR NEXT WEEK
Monday HW4
Chapter 15 – More Probability Rules.
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