Because each can occur in only one case. If you roll two, 6-sided dice the only way to get a sum of 2 is when they are BOTH 1's. The only way to get a sum of 12 is when they are both 6's. Thus these are the two least likely (most extreme) sums. For example there are two ways to get a sum of 3 (a 1 on one and a 2 on the other OR the reverse) or 11 (a 5 on one and a 6 on the other OR the reverse). There are even more ways to get 4 (1-3,3-1,2-2)...
Zero is the probability of rolling a sum of 15 on two fair dice; the maximum value is 12.
The probability of rolling 12 with 2 dice is 1 in 36. The probability of not rolling 12 with 2 dice is 35 in 36.
It is 1/12.
The probability of rolling a sum of 12 in a single roll of two dice is 1 in 36, or about 0.0278.
Rolling a sum of 15 on three rolls of a die, when the first roll is a 4, is the same as rolling a sum of 11 on the second and third roll. The probability of rolling 11 on two dice is 3 in 36, or 1 in 12.
It is 1/36.
1/36
The probability is 21/36 = 7/12
There are 36 outcomes for rolling 2 dice, and there is 1 way that a 12 can occur which is 6,6. So, the probability of rolling the sum of 12 on 2 dice is 1/36.
11/12
The probability is 1/6 x 1/6 = 1/36.
Rolling dice, there are 62 or 36 outcomes. There is only 1 way to get a 12; 6 & 6. Therefore, the probability is 1/36 or 0.0278.