posted by Brian on .
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?
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)÷(1/6)
= (1/36)(6/1) = 1/6