投擲兩枚勻稱骰子，求所擲得的兩點數之和為質數的概率。

每粒骰 1 點至 6 點，所以兩粒骰共有 36 個排列：
(1, 1) (1, 2) (1, 3) (1, 4) (1, 5) (1, 6)
(2, 1) (2, 2) (2, 3) (2, 4) (2, 5) (2, 6)
(3, 1) (3, 2) (3, 3) (3, 4) (3, 5) (3, 6)
(4, 1) (4, 2) (4, 3) (4, 4) (4, 5) (4, 6)
(5, 1) (5, 2) (5, 3) (5, 4) (5, 5) (5, 6)
(6, 1) (6, 2) (6, 3) (6, 4) (6, 5) (6, 6)

其和為質數，共有 15 個排列：
(1, 1) → 2 點
(1, 2) (2, 1) → 3 點
(1, 4) (4, 1) (2, 3) (3, 2) → 5 點
(1, 6) (6, 1) (2, 5) (5, 2) (3, 4) (4, 3) → 7 點
(5, 6) (6, 5) → 11 點

概率
= 15/36
= 5/12
=