Here are all possible rolls of a 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)
Since we are given that the sum is less than 7, we will
remove from the sample space all the ones which have sum
of 7 or more, leaving only those that have the given
property.
The reduced sample space consists of 15 rolls is this:
(1,1) (1,2) (1,3) (1,4) (1,5)
(2,1) (2,2) (2,3) (2,4)
(3,1) (3,2) (3,3)
(4,1) (4,2)
(5,1)
And I'll now color the doubles red.
(1,1) (1,2) (1,3) (1,4) (1,5)
(2,1) (2,2) (2,3) (2,4)
(3,1) (3,2) (3,3)
(4,1) (4,2)
(5,1)
So 3 out of the 15 are doubles. So the probability is 3/15,
which reduces to 1/5, to three decimal places is .200
Edwin
