Two number cubes are rolled. What is the probability of rolling a sum of 9 or a sum that is even?

1 Answer
Shwetank Mauria · EZ as pi
Feb 17, 2016

Probability of rolling a sum of 9 or a sum that is even from two number cubes is #11/18#

Explanation:

When a dice is rolled there are different ways in which #9# can be obtained, which are (3,6) or (4,5) or (5,4) or (6,3) i.e. #4# options. As in all there are #6*6=36# options, probability is #4/36# or #1/9#.

For getting an even number as sum, we can have (1,1) or (1.3) or (1,5) or (2,2) or (2,4) or (2,6) or (3,1) or (3,3) or (3,5) or (4,2) or (4,4) or (4,6) or (5,1) or (5,3) or (5,5) or (6,2) or (6,4) or (6,6) i.e. #18# options, probability is #18/36# or #1/2#.

Note that the two events (getting 9 or even sum) are mutually exclusive, the probabilities can be just added i.e. combined probability is #1/9+1/2=(2+9)/18# i.e. #11/18#

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