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Re: Pam and Robin each roll a pair of fair, six-sided dice. What is the pr [#permalink]

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06 Mar 2017, 11:47

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The answer should be D. 11/216. There are 2 cases: 1. Both dices show the same number, so it's 6 out of 36. Then for the other player the probability to roll the same number is 1/6 x 1/6. 2. There are 30 out of 36 options for the dices to be different numbers. The probability for the other player to roll the same is 2/6 x 1/6.

Probability = 1/6 x 1/6 x 1/6 + 5/6 x 2/6 x 1/6 = 11/216

Pam and Robin each roll a pair of fair, six-sided dice. What is the pr [#permalink]

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08 Mar 2017, 01:38

kolodits wrote:

The answer should be D. 11/216. There are 2 cases: 1. Both dices show the same number, so it's 6 out of 36. Then for the other player the probability to roll the same number is 1/6 x 1/6. 2. There are 30 out of 36 options for the dices to be different numbers. The probability for the other player to roll the same is 2/6 x 1/6.

Re: Pam and Robin each roll a pair of fair, six-sided dice. What is the pr [#permalink]

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08 Mar 2017, 06:42

ziyuen wrote:

kolodits wrote:

The answer should be D. 11/216. There are 2 cases: 1. Both dices show the same number, so it's 6 out of 36. Then for the other player the probability to roll the same number is 1/6 x 1/6. 2. There are 30 out of 36 options for the dices to be different numbers. The probability for the other player to roll the same is 2/6 x 1/6.

Dear kolodits, How do you able to get the value for \(\frac{2}{6}\)?

The second player roll the first dice. It should be equal to one of the dices the first player rolled. It doesn't matter which one, so there are 2 options out of 6. For the second dice there is only 1 option left, which makes it: 2/6 * 1/6.

Re: Pam and Robin each roll a pair of fair, six-sided dice. What is the pr [#permalink]

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08 Mar 2017, 07:50

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At first I misread and thought it was asking for the same sum of the pairs of dice which would yield a different answer.

There are two cases. The first is when the first person rolls two different numbers. This happens 5/6 of the time. The second is when the first person rolls the same number on both die. This happens 1/6 of the time.

In the first case, the second person has a 2/6 chance to roll one of the two numbers that the first person rolled with the first die. If the first die is one of the two numbers, then the second person only has a 1/6 chance for the second die to match up. This means that in the first case, the second person has a 2/6 * 1/6 = 1/18 chance to have the same roll. This applies 5/6 of the time.

In the second case, both dice must match, so the second person has a 1/6 chance to roll the same number with each of the two die. This means the total probability is 1/6 * 1/6 = 1/36. This applies 1/6 of the time.

This means that the total probability is 5/6*1/18 + 1/6*1/36 = 5/108 + 1/216 = 10/216 + 1/216 = 11/216. Answer is D

Pam and Robin each roll a pair of fair, six-sided dice. What is the probability that Pam and Robin will both roll the same set of two numbers?

A. 1/216

B. 1/36

C. 5/108

D. 11/216

E. 1/18

We need to determine the probability that when Pam and Robin each rolls a pair of fair, six-sided dice, they both roll the same set of numbers. There are two scenarios: when Pam and Robin both roll the same two numbers and when they roll two distinct numbers.

Scenario 1: When the two numbers on the dice are the same

Let’s say they both roll 1s. That is, Pam rolls (1, 1) and Robin rolls (1, 1). The probability of this happening is

1/6 x 1/6 x 1/6 x 1/6 = 1/(6^4)

Since the probability is the same for all 6 pairs of numbers, the probability of their rolling the same numbers is 6 x 1/(6^4) = 1/(6^3) = 1/216.

Scenario 2: When the two numbers on the dice are distinct

There are 6 x 5 = 30 ways to roll two distinct numbers when rolling two dice. Let’s say Pam rolls (1, 2) and Robin also rolls (1, 2). The probability of this happening is:

1/6 x 1/6 x 1/6 x 1/6 = 1/(6^4)

However, if Pam rolls (1, 2) and Robine rolls (2,1), those are still considered the same set of numbers, and the probability of that occurring is also 1/(6^4).

Therefore, for each pair of distinct numbers rolled, the probability is 2 x 1/(6^4) = 2/(6^4). Since there are 30 such pairs, the overall probability is 30 x 2/(6^4) = 60/(^4) = 10/(6^3) = 10/216.

Finally, since the events in option 1 and those in option 2 are mutually exclusive, we use the addition rule of probability. That is, the probability that Pam and Robin will both roll the same set of two numbers is:

1/216 + 10/216 = 11/216

Answer: D
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GMAT Quant Self-Study Course 500+ lessons 3000+ practice problems 800+ HD solutions

Pam and Robin each roll a pair of fair, six-sided dice. What is the pr [#permalink]

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26 Mar 2017, 20:58

JeffTargetTestPrep wrote:

Bunuel wrote:

Pam and Robin each roll a pair of fair, six-sided dice. What is the probability that Pam and Robin will both roll the same set of two numbers?

A. 1/216

B. 1/36

C. 5/108

D. 11/216

E. 1/18

We need to determine the probability that when Pam and Robin each rolls a pair of fair, six-sided dice, they both roll the same set of numbers. There are two scenarios: when Pam and Robin both roll the same two numbers and when they roll two distinct numbers.

Scenario 1: When the two numbers on the dice are the same

Let’s say they both roll 1s. That is, Pam rolls (1, 1) and Robin rolls (1, 1). The probability of this happening is

1/6 x 1/6 x 1/6 x 1/6 = 1/(6^4)

Since the probability is the same for all 6 pairs of numbers, the probability of their rolling the same numbers is 6 x 1/(6^4) = 1/(6^3) = 1/216.

Scenario 2: When the two numbers on the dice are distinct

There are 6 x 5 = 30 ways to roll two distinct numbers when rolling two dice. Let’s say Pam rolls (1, 2) and Robin also rolls (1, 2). The probability of this happening is:

1/6 x 1/6 x 1/6 x 1/6 = 1/(6^4)

However, if Pam rolls (1, 2) and Robine rolls (2,1), those are still considered the same set of numbers, and the probability of that occurring is also 1/(6^4).

Therefore, for each pair of distinct numbers rolled, the probability is 2 x 1/(6^4) = 2/(6^4). Since there are 30 such pairs, the overall probability is 30 x 2/(6^4) = 60/(^4) = 10/(6^3) = 10/216.

Finally, since the events in option 1 and those in option 2 are mutually exclusive, we use the addition rule of probability. That is, the probability that Pam and Robin will both roll the same set of two numbers is:

1/216 + 10/216 = 11/216

Answer: D

If we are already considering (1,2) and (2,1) to be the same set while calculating probability then why do we have total number of pairs = 30? Shouldn't it be 15?

Re: Pam and Robin each roll a pair of fair, six-sided dice. What is the pr [#permalink]

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15 Aug 2017, 01:36

jpeeples85 wrote:

At first I misread and thought it was asking for the same sum of the pairs of dice which would yield a different answer.

There are two cases. The first is when the first person rolls two different numbers. This happens 5/6 of the time. The second is when the first person rolls the same number on both die. This happens 1/6 of the time.

In the first case, the second person has a 2/6 chance to roll one of the two numbers that the first person rolled with the first die. If the first die is one of the two numbers, then the second person only has a 1/6 chance for the second die to match up. This means that in the first case, the second person has a 2/6 * 1/6 = 1/18 chance to have the same roll. This applies 5/6 of the time.

In the second case, both dice must match, so the second person has a 1/6 chance to roll the same number with each of the two die. This means the total probability is 1/6 * 1/6 = 1/36. This applies 1/6 of the time.

This means that the total probability is 5/6*1/18 + 1/6*1/36 = 5/108 + 1/216 = 10/216 + 1/216 = 11/216. Answer is D

1/6 of the time? 5/6 of the time? How are you saying that? can you please explain?