Question

A die is rolled twice. If the sum of the numbers facing upwards is even find the probability that both are odd.

Answer 1

Let A: both are odd 

A = {(1, 1) (1, 3) (1, 5) (3, 1) (3, 3) (3, 5) (5. 3) (5, 1) (5, 5)} 

n(A) = 9 

B = sum is even 

= {((1, 1) (1, 3) (1, 5) (3, 1) (3, 3) (3, 5) (5, 3) (5, 1) (5, 5) (2, 2) (2, 4) (2, 6) (4, 2) (4, 4) (4, 6) (6, 2) (6. 4) (6, 6))} 

n(B) = 18

n(A ∩ B) = 9