Question 806336
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Refer to the below table of dice results for 2 six-sided dice:

<table border="1" cellpadding="2" cellspacing="2" width="60%">
<tr>
<th width="20%">Sum</th>
<th width="20%">Ways</th>
<th width="20%"># of Ways</th>
</tr>
<tr>
<td width="20%">2</td><td width="20%">1,1</td><td width="20%">1</td>
</tr>
<tr>
<td width="20%">3</td><td width="20%">1,2; 2,1</td><td width="20%">2</td>
</tr>
<tr>
<td width="20%">4</td><td width="20%">1,3; 2,2; 3,1</td><td width="20%">3</td>
</tr>
<tr>
<td width="20%">5</td><td width="20%">1,4; 2,3; 3,2; 4,1</td><td width="20%">4</td>
</tr>
<tr>
<td width="20%">6</td><td width="20%">1,5; 2,4; 3,3; 4,2; 5,1</td><td width="20%">5</td>
</tr>
<tr>
<td width="20%">7</td><td width="20%">1,6; 2,5; 3,4; 4,3; 5,2; 6,1</td><td width="20%">6</td>
</tr>
<tr>
<td width="20%">8</td><td width="20%">2,6; 3,5; 4,4; 5,3; 6,2</td><td width="20%">5</td>
</tr>
<tr>
<td width="20%">9</td><td width="20%">3,6; 4,5; 5,4; 6,3</td><td width="20%">4</td>
</tr>
<tr>
<td width="20%">10</td><td width="20%">4,6; 5,5; 6,4</td><td width="20%">3</td>
</tr>
<tr>
<td width="20%">11</td><td width="20%">5,6; 6,5</td><td width="20%">2</td>
</tr>
<tr>
<td width="20%">12</td><td width="20%">6,6</td><td width="20%">1</td>
</tr>
</table>


Note that there are 36 different possible results, 6 of which are doubles, 2 of which are 3, and one of which is 12.  However, the 12 result is also doubles.  Because you don't specify what happens when a 12 is rolled (score 15 for the 12 which overrides the doubles or score 5 for the doubles which overrides the 12, or score 20 for meeting both criteria), I'm going to go with a literal interpretation of the given rules: The player gets 5 for rolling doubles AND 15 for rolling 12.


So the probability of rolling doubles OTHER than 2 sixes = 12 is *[tex \LARGE \frac{5}{6}], the probability of rolling 12 is *[tex \LARGE \frac{1}{36}], the probability of rolling 3 is *[tex \LARGE \frac{1}{18}], and the probability of rolling anything else, which we must presume represents a loss of the initial $3 wager, is *[tex \LARGE \frac{7}{9}] (28 ways to lose out of 36 outcomes).


And then the expected payout is:


*[tex \LARGE \ \ \ \ \ \ \ \ \ 5*\frac{5}{36}\ +\ 20*\frac{1}{36}\ +\ 15*\frac{1}{18}\ -\ 3*\frac{7}{9}]


You can do your own arithmetic, but in the long run you lose a quarter every time you play.


John
*[tex \LARGE e^{i\pi}\ +\ 1\ =\ 0]
<font face="Math1" size="+2">Egw to Beta kai to Sigma</font>
My calculator said it, I believe it, that settles it
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