If 2 six sided dice are tossed. What is the probability that the sum is 2 or 12?
It is the probability of 2 PLUS the probability of 12.
The only possible case of getting a 2 is {1,1}. The probability of doubles 1's is 1/36=(1/6)(1/6).
Similiarly the probability of getting a 12 is 1/36.
The sum is,
1/36+1/36=2/36=1/18