Question

Suppose we roll a pair of fair dice, let A=the numbers I rolled add up to exactly 8, and let B=the numbers I rolled multiply to an even number. Find P(Ac and Bc).

Answer 1

P(Ac and Bc) = 7/36 = 0.1944 = 19.44%

Explanation:

A probability is the number of desired outcomes divided by the number of total outcomes.

Possible outcomes:

For the pair of dice:

(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)

So 36 total outcomes.

Find P(Ac and Bc).

Complement of A(The result of the sum is different of 8) and complement of B(multiply to odd number). So the desired events are:

(1,1), (1,3), (1,5)

(3,1), (3,3)

(5,1), (5,5)

7 desired outcomes. So

P(Ac and Bc) = 7/36 = 0.1944 = 19.44%