Probabilities

Question

An ordinary (fair) die is a cube with the numbers through on the sides (represented by painted spots). Imagine that such a die is rolled twice in succession and that the face values of the two rolls are added together. This sum is recorded as the outcome of a single trial of a random experiment.Compute the probability of each of the following events:

Event : The sum is greater than 8 .
Event : The sum is divisible by 2 .

Answer 1

For a pair of fair dice, the totals occurring and their # of ways of being achieved, out of a total of 36 possible outcomes, is

 

Sum Freq

2       1

3       2

4       3

5       4

6       5

7       6

8       5

9       4

10     3

11     2

12     1

 

P(sum > 8) = (4+3+2+1)/36 = 10/36 = 5/18.

P(even total) = (1+3+5+5+3+1) = 18/36 = 1/2.