Question

5. Two unbiased dice are rolled. Calculate the probability that the sum of the two dice is:

ws
(a) 4
(b) 7
(c) Less than 7

Answer 1

The sample space has 36 possible pairs from 1,1 1,2 1,3 up to 6,5 and 6,6

(a). Three pairs add to 4 1,3 2,2 and 3,1 so P(4) = 3/36 = 1/12

(b). 6 pairs add to 7 so P(7) = 6/36 = 1/6

(c) 15 pairs add to less than 7 so P(<7) = 15/36 = 5/12