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A cube with its sides numbered 1 through 6 is rolled twice [#permalink]
28 Apr 2012, 05:33

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Difficulty:

55% (hard)

Question Stats:

58% (02:32) correct
42% (01:49) wrong based on 69 sessions

A cube with its sides numbered 1 through 6 is rolled twice, first landing on a and then landing on b. If any roll of the cube yields an equal chance of landing on any of the numbers 1 through 6, what is the probability that a + b is prime?

(A) 0 (B) 1/12 (C) 5/12 (D) 7/18 (E) 4/9

I am not sure if the OA is correct. Thanks for help !

Re: A cube with its sides numbered 1 through 6 is rolled twice [#permalink]
28 Apr 2012, 05:50

Expert's post

qtrip wrote:

A cube with its sides numbered 1 through 6 is rolled twice, first landing on a and then landing on b. If any roll of the cube yields an equal chance of landing on any of the numbers 1 through 6, what is the probability that a + b is prime?

(A) 0 (B) 1/12 (C) 5/12 (D) 7/18 (E) 4/9

I am not sure if the OA is correct. Thanks for help !

Re: A cube with its sides numbered 1 through 6 is rolled twice [#permalink]
13 Apr 2014, 01:13

Bunuel wrote:

qtrip wrote:

A cube with its sides numbered 1 through 6 is rolled twice, first landing on a and then landing on b. If any roll of the cube yields an equal chance of landing on any of the numbers 1 through 6, what is the probability that a + b is prime?

(A) 0 (B) 1/12 (C) 5/12 (D) 7/18 (E) 4/9

I am not sure if the OA is correct. Thanks for help !

The question says "first landing on a and then landing on b" so I assumed that the result in both rolls of the dice had to be different, so I didn't count 1,1. So for me answer was D. Was my assumption wrong?

Re: A cube with its sides numbered 1 through 6 is rolled twice [#permalink]
13 Apr 2014, 01:21

NAL9 wrote:

Bunuel wrote:

qtrip wrote:

A cube with its sides numbered 1 through 6 is rolled twice, first landing on a and then landing on b. If any roll of the cube yields an equal chance of landing on any of the numbers 1 through 6, what is the probability that a + b is prime?

(A) 0 (B) 1/12 (C) 5/12 (D) 7/18 (E) 4/9

I am not sure if the OA is correct. Thanks for help !

The question says "first landing on a and then landing on b" so I assumed that the result in both rolls of the dice had to be different, so I didn't count 1,1. So for me answer was D. Was my assumption wrong?

Question says the roll landed on a and b, a and b can be different or same. The question does not give any idea about that, so assuming they are different is not correct in my opinion.

Re: A cube with its sides numbered 1 through 6 is rolled twice [#permalink]
13 Apr 2014, 05:27

Expert's post

NAL9 wrote:

Bunuel wrote:

qtrip wrote:

A cube with its sides numbered 1 through 6 is rolled twice, first landing on a and then landing on b. If any roll of the cube yields an equal chance of landing on any of the numbers 1 through 6, what is the probability that a + b is prime?

(A) 0 (B) 1/12 (C) 5/12 (D) 7/18 (E) 4/9

I am not sure if the OA is correct. Thanks for help !

The question says "first landing on a and then landing on b" so I assumed that the result in both rolls of the dice had to be different, so I didn't count 1,1. So for me answer was D. Was my assumption wrong?

Unless it is explicitly stated otherwise, different variables CAN represent the same number. _________________