If you roll 2 die, what is the probability that you will get a sum of 11? What about a sum of 5?

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Answer 1 · 2015-11-18T11:37:40

The probabilities are: $P (A) = \frac{1}{18}$ $P(A)=1/18$ ; $P (B) = \frac{1}{9}$ $P(B)=1/9$ .

To calculate the probabilities we have to calculate the number of all elementary events first.

$bar(bar(Omega))=6^2=36$

Event $A$ -"sum of numbers is 11" consist of 2 elements:

$A={(6,5);(5,6)}$ ,

so $P(A)=2/36=1/18$

Event $B$ -"a sum of numbers is 5" consist of 4 elements:

$B={(1,4);(2,3);(3,2);(4,1)}$

so $P(B)=4/36=1/9$