Question

Two dies are thrown simultaneously and the sum of the numbers obtained is found to be 7. What is the probability that the number 3 has appeared at least once.

• A. 1/6
• B. 2/5
• C. 1/3
• D. 1/4

Answer 1

Answer:

C. 1/3

A = { (1,6) ( 6, 1) ( 2,5) (5,2) (3,4) (4,3) } B = { (1, 3) ( 2, 3) ( 3, 1) ( 3 ,2) ( 3, 3) ( 3, 4) ( 3, 5) ( 3, 6) (4, 3) ( 5, 3) (6, 3) } P(B | A) = P( A ∩ B)/P(A) = (2/36)/(6/36) = 2/6 = 1/3