Addition Rule
What is the probability that you roll a total of 7 or 11 when you roll two dice? Enter your answer as a decimal with two significant figures.
The events of rolling a 7 and rolling a 11 are disjoint so we can add the probabilities of each to get the answer.
First, there are 6\(\cdot\)6=36 total outcomes for rolling two dice, and each outcome is equally likely to occur.
The event of the dice totalling 7 consists of the 6 outcomes (1,6), (2,5), (3,4), (4,3), (5,2), and (6,1).
The probability of this event is therefore 6/36 = 1/6. The event of the dice totalling 11 consists of the 2 outcomes (5,6) and (6,5).
The probability of this event is 2/36 = 1/18. Adding the two up, 1/6 + 1/18 = 2/9.