In: Statistics and Probability
In the carnival game Under-or-Over-Seven, a pair of fair dice is rolled once, and the resulting sum determines whether the player wins or loses his or her bet. For example, using method one, the player can bet $2.00 that the sum will be under 7, that is, 2, 3, 4, 5, or 6. For this bet, the player wins $2.00 if the result is under 7 and loses $2.00 if the outcome equals or is greater than 7. Similarly, using method two, the player can bet $2.00 that the sum will be over 7, that is, 8, 9, 10, 11, or 12. Here, the player wins $2.00 if the result is over 7 but loses $2.00 if the result is 7 or under. A third method of play is to bet $2.00 on the outcome 7. For this bet, the player wins $8.00 if the result of the roll is 7 and loses $2.00 otherwise.
Outcomes of a two dice roll |
1 |
2 |
3 |
4 |
5 |
6 |
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1 |
2 |
3 |
4 |
5 |
6 |
7 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
a. Construct the probability distribution representing the different outcomes that are possible for a $2.00 bet using method one.
X |
P(X) |
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(Type an exact answer in simplified form.)
b. Construct the probability distribution representing the different outcomes that are possible for a $2.00 bet using method two.
X |
P(X) |
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(Type an exact answer in simplified form.)
c. Construct the probability distribution representing the different outcomes that are possible for a $2.00 bet using method three.
X |
P(X) |
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(Type an exact answer in simplified form.)
d. What is the expected long-run profit (or loss) to the player for each of the three methods of play?
Method one expected profit (or loss) |
muμ |
equals= |
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Method two expected profit (or loss) |
muμ |
equals= |
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Method three expected profit (or loss) |
muμ |
equals= |
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$(Round to the nearest cent as needed.) |
a)
There are 36 outcomes one would get for rolling a pair of fair dice. For sum to be under 7, the possible outcomes are, 2, 3, 4, 5 and 6. The probabilities of the outcomes are 1/36, 2/36, 3/36, 4/36, 5/36. Assume, the r.v denote the sum of the outcome of dice. Therefore,
the P(X<=6)=1/36+2/36+3/36+4/36+5/36 = 5/12
The sum of 7 or more are 7, 8, 9, 10, 11 and 12.
Thus, P(X>=7)=6/36+5/36+4/36+3/36+2/36+1/36 = 7/12
P($2)=0.4167
P(-$2)=0.5833
b)
Out of 36 outcomes 21 has sum less than 7 or less. So the probability of getting a sum 7 or less than 7 is
P(sum equal to or less than 7) = 21/ 36
And probability of getting a sum of over 7 is
P(sum over 7) = 15/36
c)
X = Outcome of the bet of Method 3 in $
There are two possible values of X :
i) $16 if he wins the bet.
ii) - $4, if he loses the bet.
P(X = +16) = P(rolling a 7)
P(X = +16) = 6/36
P(X = -4) = P(rolling any number but 7)
P(X = -4) = 1 - P(rolling a 7) = 1 - 6/36 = 30/36
Answer: Probability distribution of X (Method Three) =
X | P(X) |
8 | 6/36 |
-2 | 30/36 |
d)
Expected value of X = E(X) =
For Method one : Expected profit (or loss) = (4 x 15/36) + (-4 x 21/36) = -24/36 = -2/3
Ans: In Method one, there is an expected loss of $(2/3) = $0.67 = 67 cents.
For Method two : Expected profit (or loss) = (4 x 15/36) + (-4 x 21/36) = -24/36 = -2/3
Ans: In Method two, there is an expected loss of $(2/3) = $0.67 = 67 cents.
For Method three : Expected profit (or loss) = (16 x 6/36) + (-4 x 30/36) = -24/36 = -2/3
Ans: In Method three, there is an expected loss of $(2/3) = $0.67 = 67 cents.
So, we see that in the long run, all the three methods have exactly the same expected loss = 67 cents.