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# Help Me Understand this problem. ( I'm asking for help and advice )

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Jackie rolls two fair, six-sided dice. You are not told what the rolls were, but you are told that the sum of the two rolls is a prime. What is the probability that the sum of the two rolls is 5?

Mar 16, 2020

#1
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Possible

primes.        Die 1.     Die 2.

2.              1.            1

3.              1.            2

2.            1

5.              1.            4

4.            1

2.            3

3.            2

7.              1.            6

6.            1

2.            5

5.            2

3.            4

4.            3

11.            5.            6

6.            5

There are 4 ways to make 5 out of 15 ways to make a prime.

Mar 16, 2020
#2
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Thanks! I think I understand now!

Mar 16, 2020
#3
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Wait, so 4/5 of 15 ways. That's 4/75, and I've already tried the answer before.

Mar 16, 2020
#4
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No! There are 4 possibilities out of a total of 15, so the probability is 4/15.

Alan  Mar 16, 2020
#5
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Ohhhh, sorry, my brain is not working today. Thanks for teaching me and letting me understand!

Mar 16, 2020