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Analysis. A dice problem Here is an oft-posed question. Can you construct a pair of dice other than the usual ones with 1, 2, 3,

Analysis. A dice problem

"Here is an oft-posed question. Can you construct a pair of dice other than the usual ones with 1, 2, 3, 4, 5, 6 on the faces so that the resultant probabilities are the same? First, we construct the usual addition chart and its frequency chart."

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"The entry 6, for example, indicates that there are 6 ways to achieve a total of 7.

Now suppose you have two die with the following face numbers: 1, 2, 2, 3, 3, 4 on one die and 1, 3, 4, 5, 6, 8 on the other die. As before we will construct the addition table and its frequency chart."

+ 1 3 4 5 6 8
1 2 4 5 6 7 9
2 3 5 6 7 8 10
2 3 5 6 7 8 10
3 4 6 7 8 9 11
3 4 6 7 8 9 11
4 5 7 8 9 10 12

sum 2 3 4 5 6 7 8 9 10 11 12
freq 1 2 3 4 1

"The reader should complete this frequency chart to discover a surprising result.

Why did this happen? Will this happen with other dice configurations? Let's look at the underlying algebra."

"The generating function x1 + x2 + x3 + x4 + x5 + x6gives the outcomes of one die ; just look at the exponents. For two dice look at the product (or square):"

(x1 + x2 + x3 + x4 + x5 + x6)2 =

1x2 + 2x3 + 3x4 + 4x5 + 5x6 + 6x7 + 5x8 + 4x9 + 3x10 + 2x11 +x12.

"Those coefficients are exactly the numbers in the frequency chart for a pair of regular dice! On a craps table in Las Vegas 7 is a special outcome when tossing a pair of dice; there are 6 ways it can happen:"

(1, 6), (2, 5), (3, 4), (4, 3), (5, 2), (6, 1).

"An alternate factorization of our 12th degree polynomial could reveal a "new dice" pair. Start with

x + x2 + x3 + x4 + x5 + x6 =

x (1 + x + x2 + x3 + x4 + x5) = x () = x(1 + x3) = x (1 + x + x2)(1 + x)(1 - x + x2).

Remember this is just for one die. A "new pair" of factors must multiply to the square of this 6th degree polynomial or in other words, to"

x2(1 + x + x2)(1 + x)2(1 - x + x2)2 .

"So we have eight factors to allocate to two die, keeping in mind that the factors have to behave. Each of the two ways of factoring must have an x to maintain positive outcomes. Each factor must have a 1 + x and 1 + x + x2 so that you have 6 faces, by letting x = 1. So there are not many options. In fact, there are just two ways of allocating the remaining two factors: 1 - x + x2 and 1 - x + x2. Here they are:"

  1. Allocate one to each die

x (1 + x + x2)(1 + x)(1 - x + x2) = x + x2 + x3 + x4+ x5 + x6

and the same for the second die

  1. Allocate both to one die

x (1 + x + x2)(1 + x)( 1 - x + x2)2 = x + x3 + x4 + x5 + x6+ x8

and the second die gets

x (1 + x + x2)(1 + x) = x + 2x2 + 2x3 + x4

"The first die has 1, 3, 4, 5, 6, 8 on its faces, and the second has 1, 2, 2, 3, 3, 4 on its six faces.

This new pair of dice is called Sicherman (1978 issue of Scientific American - Martin Gardner)dice or "weird dice".

Our tables show that rolling a particular sum is the same using either pair of dice. But this is not so when rolling doubles. With the usual pair of dice there are 6 ways to roll a double: (1, 1), (2, 2), (3, 3), (4, 4), (5, 5), and (6, 6), so the probability is 6/36. The "new pair" has just 4 ways to roll a double:

(1, 1), (3, 3), (3, 3) and (4, 4). The new probability is 4/36.

Also, if you allow 0 to be on a face the following pairs are produced:

011223 and 245679 ; 233445 and 023457."

Question

Label the four faces of a pair of dice in the shape of a regular tetrahedron with the integers 1, 2, 3, 4. Make both tables and reproduce the analysisabove.

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