Section: Mathematics

20) If you roll two standard dice, what is the probability that the sum of their spot values will be a prime number?

1. 7/18
2. 13/36
3. 1/4
4. 7/12
5. 5/12

There is one way to roll a total of 2 (1 and 1), two ways to roll a total of 3 (1 and 2, or 2 and 1), four ways to roll a total of 5 (1 and 4, 4 and 1, 2 and 3, or 3 and 2) six ways to roll a seven, and two ways to roll an eleven. This makes a total of twenty-one ways to roll a prime number total. This creates a probability of 15/36, which reduces to 5/12.