Step-by-step explanation:
there are 36 (6×6) possible results and number combinations for 2 dice.
a)
to create a sum of 4 we need one of the following combinations :
1 3
2 2
3 1
so, 3 out of the overall possible 36 possibilities.
and that means the probability is 3/36 = 1/12
b)
to create a sum of 7 we need one of the following combinations :
1 6
2 5
3 4
4 3
5 2
6 1
so, 6 out of the overall possible 36 possibilities.
and that means a probability of 6/36 = 1/6
c)
since the possible outcomes in that regard are only 2 (even and uneven), with equal balance the probability is 1/2.
make it more formal ?
to get an even sum, every possible number on one die can be combined with 3 possibilities on the other.
1 can be combined with 1, 3, 5
2 with 2, 4, 6
3 with 1, 3, 5
4 with 2, 4, 6
5 with 1, 3, 5
6 with 2, 4, 6
these are 6×3 = 18 combinations of of the possible 36.
so, the probability is 18/36 = 1/2
d)
not a 6 ?
so, what does that mean ?
we are looking only at 5 possible outcomes per die.
that is 5×5 = 25 combinations out of the possible 36.
that means that probabilty is 25/36.
e)
not a perfect square ?
we have in the range of the possible sums with 2 dice (2 .. 12) only two perfect squares : 4 and 9
so, the sum must NOT be 4 AND NOT be 9.
so, here it might be easier to count the unwanted cases and then deduct the probability from 1 to express the opposite.
the combinations to get 4 we have already under a)
3 combinations with 3/36=1/12 probability.
the combinations to get 9
1 none
2 none
3 6
4 5
5 4
6 3
so, 4 combinations with a probability of 4/36 = 1/9
therefore, we have (3+4) = 7 cases out of the possible 36 we actually want to avoid.
so, the probability to get any one of the other (desired) combinations is therefore (36-7)/36 = 29/36
