Question

You are rolling two 6-sided dice and examining the sum of the two dice (for example, if you roll a 3 and a 5, this is an 8).

a) What is the probability of rolling a sum of 7?
b) What is the probability of rolling a sum of 11?
c) What is the probability of rolling a sum of 7 or 11?
d) What is the probability of rolling a sum of 7 and 11?

Answer 1

make a table showing all of the possible outcomes.

1 1
1 2
1 3
...
6 5
6 6

count the number of outcomes that satisfy your question, then divide by the number of lines in the table. The result is the probability.

For example, consider flipping two coins. Possible outcomes are:

H H
H T
T H
T T

a total of 4 possible outcomes

the probability of getting two coins both heads up (H H) is 1/4
the probability of getting one heads and one tails (H T or T H) is 2/4
the probability of getting two both tails (T T) is 1/4