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When a fair dice is rolled twice, there are 6*6 = 36 different possible outcomes (pairs of positive integer
numbers (a,b), where "a" and "b" are from 1 to 6, inclusive).
These outcomes have the same probability each.
The sum of 8 have these 5 outcomes
(2,6), (3,5), (4,4), (5,3), (6,2).
The sum of 11 have these 2 outcomes
(5,6), (6,5).
Therefore, P(8 or 11) = P(8) + P(11) = + = .
It is the answer to part (a).
Solved.
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Regarding part (b), let me tell you that I don't like VERY MUCH to have more that one question in the post.
It is because I DON'T WANT my response becomes a mess.
Make your conclusion/conclusions . . .
Also, I firmly believe, that, when the visitor put many question in his (or her) post, it only means
that the visitor does not want to learn the subject, at all; it only means that the visitor wants
the tutors work INSTEAD of HIM (or HER).
Therefore, I always say that those who put more than one problem/question into the post, work AGAINST their own interests.