# math/probability

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If two fair dice are rolled, find the probability of a sum of 6 given that the roll is a "double".

How do I do this?

• math/probability -

let A be "sum of 6" and B be "double"

What you have is P(A│B) , read as
the probability of A given B
which is defined as P(A AND B)/P(B)

Prob(A AND B) = Prob(sum of 6 AND a double) = 1/36
Prob(B) = 6/36 = 1/6

so Prob(sum of 6 AND a double) = (1/36)รท(1/6)
= (1/36)(6/1) = 1/6

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