Henry Ernest Dudeney/Modern Puzzles/205 - The Three Dice

by : $205$

 * The Three Dice
 * Mason and Jackson were playing with three dice.
 * The player won whenever the numbers thrown added up to one of the two numbers he selected at the beginning of the game.
 * As a matter of fact, Mason selected $7$ and $13$, and one of his winning throws was $6$, $4$, $3$.
 * What were his chances of winning a throw?
 * And what two other numbers should Jackson have selected for his own throws to make his chances of winning exactly equal?