+0  
 
+1
216
5
avatar+172 

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
avatar+31340 
+2

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
avatar+172 
+1

Thanks! I think I understand now!

 Mar 16, 2020
 #3
avatar+172 
+1

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

 Mar 16, 2020
 #4
avatar+31340 
+2

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

Alan  Mar 16, 2020
 #5
avatar+172 
+1

Ohhhh, sorry, my brain is not working today. Thanks for teaching me and letting me understand!

 Mar 16, 2020

72 Online Users

avatar
avatar
avatar
avatar