Ta có: Ω = {(a, b, c); 1 ≤ a, b, c ≤ 3}, suy ra n(Ω) = 3.3.3 = 27.

Ta có: A = {(1; 2; 3); (1; 3; 2); (2; 1; 3); (2; 3; 1); (3; 1; 2); (3; 2; 1); (2; 2; 2)}.

Do đó n(A) = 7, suy ra P(A) = \(\frac{7}\).

           B = {(1; 1; 1); (2; 2; 2); (3; 3; 3)}.

Do đó, n(B) = 3, suy ra P(B) = \(\frac{3} = \frac{1}{9}\).

Có A ∩ B ={(2; 2; 2)}, suy ra P(AB) = \(\frac{1}\).

Như vậy, P(A | B) = \(\frac{{P\left( {AB} \right)}}{{P\left( B \right)}} = \frac{1}{3}\);

                P(B | A) = \(\frac{{P\left( {AB} \right)}}{{P\left( A \right)}} = \frac{1}{7}\).