Answer:
1/24 = 0.041666666...
Explanation:
when rolling 4 dice, we have
6 × 6 × 6 × 6 = 6⁴ = 1296
different possible outcomes (each die has 6 possible outcomes).
so, the probability of any particular pattern is then
1/1296.
we need to find how many patterns there are to represent the desired result of 2 identical odd numbers combined with 2 identical even numbers.
there are on every die 3 out of 6 options for an odd number, and the other 3 out of 6 options for an even number.
when we roll 2 dice, the patterns for 2 identical odd numbers are
1 1
3 3
5 5
so, 3 out of the possible 36.
similar for 2 identical even numbers.
2 2
4 4
6 6
3 out of the possible 36.
so, combining this together for a roll of 4 dice, we get then
3 × 3 out of the possible 36 × 36
9 out of the possible 1296 patterns.
that means the probability (desired over total possible cases) for a specific combination of 2-and-2 dice is
9/1296 = 1/144 = 0.006944444...
but there are 4! / (2! × 2!) = 6 possibilities (pick 2 out of 4, where the sequence of the picked ones does not matter) to pick 2 dice out of 4 and to show the same pattern across the 4 dice, as e.g. for the basic pattern 1 1 2 2 we can have
1 1 2 2
1 2 1 2
1 2 2 1
2 1 2 1
2 1 1 2
2 2 1 1
all of the 9 patterns have these 6 combination possibilities.
so, we need to multiply the individual pattern probability by 6 for the total probability
1/144 × 6 = 6/144 = 1/24 = 0.041666666...