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Re: John rolls a fair six-sided die with faces numbered 1 throug [#permalink]
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Answer: B
The first thing that should be considered here is that these two statements are not complementary:
Probability of a side to be even: P(E)
Probability of a side to be odd: P(O)
A: P(E and E)
B: P(E and O) + P(O and E) + P(E and E) = 1 - P(O and O)
Total possible occurrences: 6*6 = 36

As P(E and O) and P(O and E) can’t be negative, seemingly B is larger than A. But let’s try:
A: P(E and E) = 9/36 = 1/4
(2 | 4 | 6, 2| 4| 6) -> (2,2), (2,4),(2,6), (4,2), …, (6,6) [9 ones]

B: P(E and O) + P(O and E) + P(E and E) = 3 * 9/36 = 3/4

P(E and O) = 9/36
(2|4|6, 1,3,5) -> 3*3 = 9
P(O and E) = 9/36
(1,3,5, 2|4|6) -> 3*3 = 9
P(E and E)= 9/36

So B is bigger than A.
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Re: John rolls a fair six-sided die with faces numbered 1 throug [#permalink]
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GREsucks wrote:
chetan2u wrote:



John rolls a fair six-sided die with faces numbered 1 through 6 twice.

Quantity A
Quantity B
The probability that both rolls are even
The probability that both rolls are not odd



A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given.


--------CONCEPT---------

In probability, especially dices, there are always very limited outcomes with a particular logic
So, only 4 possibilities in throwing 2 dices exist:

1. Both even
2. Both odd
3. First even & Then odd
4. First odd then even

So, both even probability = 1/4
And both not odd probability = 4/4 - 1/4 = 3/4

Hence, B>A......option B



That's great concept.

But I would like to mention one point

Since the number of odds = no. of even, in the fair six sided dice

SO once we get the probability that both are even = \(\frac{1}{4}\)= probability of both are odd

Hence the probability of both not odd (As per complement rule) = \(1 - \frac{1}{4} = \frac{3}{4}\)
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Re: John rolls a fair six-sided die with faces numbered 1 throug [#permalink]
nice question
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Re: John rolls a fair six-sided die with faces numbered 1 throug [#permalink]
this question is GRE-level. Nice
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Re: John rolls a fair six-sided die with faces numbered 1 throug [#permalink]
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John rolls a fair six-sided die with faces numbered 1 through 6 twice.

Quantity A
Quantity B
The probability that both rolls are even
The probability that both rolls are not odd



A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given.[/quote]

--------CONCEPT---------

In probability, especially dices, there are always very limited outcomes with a particular logic
So, only 4 possibilities in throwing 2 dices exist:

1. Both even
2. Both odd
3. First even & Then odd
4. First odd then even

So, both even probability = 1/4
And both not odd probability = 4/4 - 1/4 = 3/4

Hence, B>A......option B[/quote]


very helpful logic and concept.
Thanks for sharing.
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John rolls a fair six-sided die with faces numbered 1 throug [#permalink]
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This question is worded poorly from a grammar perspective, such that one could plainly read it as meaning the probability that neither role contains an odd, as opposed to one odd and one even being permitted. In plain English, if someone says to me, "both of my socks are not green," I would not read that as one could be green and one could be red. I would read that as them telling me neither is green. The GRE would not write a question which was ambiguous in this manner. I think what they mean for B, if they want to allow for the possibility of one odd and one even, is "the probability that at least one of the rolls is not odd," which is not ambiguous.
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John rolls a fair six-sided die with faces numbered 1 throug [#permalink]
Given that John rolls a fair six-sided die with faces numbered 1 through 6 twice.

As we are rolling two dice => Number of cases = \(6^2\) = 36

Quantity A: The probability that both rolls are even

Probability of getting an even number in any roll = \(\frac{3}{6}\) (As there are three even numbers 2, 4, 6 out of the 6 numbers) = \(\frac{1}{2}\)

=> Probability that both rolls are even = \(\frac{1}{2}\) * \(\frac{1}{2}\) = \(\frac{1}{4}\) = 0.25

Quantity B: The probability that both rolls are not odd

Probability that both rolls are not odd = 1 - P(Both odd)

Probability of getting an odd number in any roll = \(\frac{3}{6}\) (As there are three even numbers 2, 4, 6 out of the 6 numbers) = \(\frac{1}{2}\)

=> Probability that both rolls are odd = \(\frac{1}{2}\) * \(\frac{1}{2}\) = \(\frac{1}{4}\)

=> Probability that both rolls are not odd = 1 - P(Both odd) = 1 - \(\frac{1}{4}\) = \(\frac{3}{4}\) = 0.75

Clearly, Quantity B(0.75) > Quantity A(0.25)

So, Answer will be B
Hope it helps!

Watch the following video to learn How to Solve Dice Rolling Probability Problems

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Re: John rolls a fair six-sided die with faces numbered 1 throug [#permalink]
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