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M07-18

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Re: M07-18 [#permalink]

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New post 01 Apr 2017, 06:09
jwang516 wrote:
I get the solution but what confused me was the possibility of a third type of snake that is NOT viper or Cobra. I thought the question stem left that possibility open

"There is at least one viper and at least one cobra in Pandora's box"- could mean that there is 1 Viper, 1 cobra and another type of snake.....nowhere does it say that the box only contains cobra and vipers

^ If this is the case. Should we always assume that it contains just cobra and viper? I don't remember where but there was a similar question maybe on OG where an answer was not sufficient because you couldn't assume a box only holds X and Y unless it specifically said so

As such, statement A could mean that you can get 1 Viper and 1 Cobra or 1 Viper and a third type of snake, no?


This is also explained on previous pages. The stem clearly says that "There is at least one viper and at least one cobra in Pandora's box".

(1) says: From any two snakes from Pandora's box at least one is a viper. There cannot be any other type of snake in the box because we know that there is at least one viper and at least one cobra and if there is some other type snake there then we can choose cobra and that snake and the condition will be violated.
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M07-18 [#permalink]

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New post 26 Apr 2017, 06:05
without total number how can you evaluate that how many cobras in there ?

option A

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Re: M07-18 [#permalink]

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the Question Stem says that there is at least 1 viper and at least 1 cobra. It doesn’t state anything else. So basically it is giving us the Minimum number of cobras and vipers.

Now, the first option states that, whenever randomly you select two snakes from the box, at least one is definitely a viper.  The meaning of the statement is that whenever randomly you pick up two snakes, either it will be one viper or it will be 2 vipers.

So we have a very interesting observation here ==> if at all there were more than one cobra in the box, there would have been at least one random scenario when both the picked up snakes would be cobras. But as it is given in the first statement, no matter how you pick two snakes, maximum number of Cobras can always only be 1.  This clearly indicates that, the maximum possible number of Cobras in the box is 1. And it has been given in the question stem that the minimum number of cobras is 1. So when we know that the maximum and minimum number of Cobras in the box is 1, it is clear that the number of Cobras in the box is 1.

Hence this option is sufficient.

The second option gives us the total number of snakes. It is definitely not possible to find a number of Cobras from this number. Hence this option is insufficient.

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New post 18 Jun 2017, 12:20
I think this is a poor-quality question and I don't agree with the explanation. For any two snakes from the box, if at least 1 is a viper, that means for any two snakes they are either 1 viper 1 cobra, or 2 vipers zero cobras. How in the world does that imply there is just one cobra. There are so many different combinations that are possible, insufficient.

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New post 18 Jun 2017, 12:25
aishakar wrote:
I think this is a poor-quality question and I don't agree with the explanation. For any two snakes from the box, if at least 1 is a viper, that means for any two snakes they are either 1 viper 1 cobra, or 2 vipers zero cobras. How in the world does that imply there is just one cobra. There are so many different combinations that are possible, insufficient.


You should read question more carefully.

The question clearly says that "There is at least one viper and at least one cobra in Pandora's box".
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New post 18 Jun 2017, 13:45
ran787 wrote:
the Question Stem says that there is at least 1 viper and at least 1 cobra. It doesn’t state anything else. So basically it is giving us the Minimum number of cobras and vipers.

Now, the first option states that, whenever randomly you select two snakes from the box, at least one is definitely a viper.  The meaning of the statement is that whenever randomly you pick up two snakes, either it will be one viper or it will be 2 vipers.

So we have a very interesting observation here ==> if at all there were more than one cobra in the box, there would have been at least one random scenario when both the picked up snakes would be cobras. But as it is given in the first statement, no matter how you pick two snakes, maximum number of Cobras can always only be 1.  This clearly indicates that, the maximum possible number of Cobras in the box is 1. And it has been given in the question stem that the minimum number of cobras is 1. So when we know that the maximum and minimum number of Cobras in the box is 1, it is clear that the number of Cobras in the box is 1.

Hence this option is sufficient.

The second option gives us the total number of snakes. It is definitely not possible to find a number of Cobras from this number. Hence this option is insufficient.


this explanation was useful and well explained, thank you for going beyond reiterating the question stem.

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New post 28 Jun 2017, 01:09
I think this is a high-quality question and I agree with explanation.

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New post 29 Jun 2017, 04:26
Hi Bunnel,

Please help me understand the flaw in my logic, I understand that from the 1st question the number of snakes in the box can be ONLY 2, that's the only way to have 1 viper and 1 cobra, however, I fail to understand that why anybody hasn't considered any other snake than viper or cobra.

Example : If I have a viper, cobra and black mamba - Using statement 1 I pick 2 snakes and I draw a viper and black mamba, the 1st statement is satisfied, however, it does not help me get the number of cobras.

I have gone through the OG problems and in some problems the OE does mention content, which is not stated in the question. Could you please help ??

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New post 29 Jun 2017, 04:34
anuj11 wrote:
Hi Bunnel,

Please help me understand the flaw in my logic, I understand that from the 1st question the number of snakes in the box can be ONLY 2, that's the only way to have 1 viper and 1 cobra, however, I fail to understand that why anybody hasn't considered any other snake than viper or cobra.

Example : If I have a viper, cobra and black mamba - Using statement 1 I pick 2 snakes and I draw a viper and black mamba, the 1st statement is satisfied, however, it does not help me get the number of cobras.

I have gone through the OG problems and in some problems the OE does mention content, which is not stated in the question. Could you please help ??


1. It's not necessary the box to have 1 viper and 1 cobra. The box can have 1 cobra and any number of vipers more than or equal to 1. The solution even gives an example: 1 cobra and 1 viper or 1 cobra and 99 vipers.

2. About some other types of snakes. This is also addressed in the thread. (1) says: From any two snakes from Pandora's box at least one is a viper. There cannot be any other type of snake in the box because we know that there is at least one viper and at least one cobra and if there is some other type snake there then we can choose cobra and that snake and the condition will be violated.
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Re: M07-18 [#permalink]

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New post 30 Jun 2017, 02:10
Bunuel wrote:
Official Solution:


This is a hard question that challenges test-taker's logic. It is simple once you understand it but hard if you have never solved it. If you made a mistake on this question, make sure you understand the logic so you can be armed with this new tool for the real test.

(1) Statement 1 tells us that from any two snakes from Pandora's box at least one is a viper. This does not mean that there are 2 snakes in the box or that there is only 1 viper. Instead, it indicates that at most, there is 1 cobra. This may mean 1 cobra and 1 viper or 1 cobra and 99 vipers. Make sure you understand this distinction. S1 tells us that there is only 1 cobra in the box, which is sufficient.

(2) The total number of snakes Pandora's box is 99. Clearly insufficient.


Answer: A



Dear Bunuel

I went along the thread but I could not understand something about fact 1.

If I use info in Fact 2 in Fact 1, it says 'at least 1 Viber' and throw them away. It means I can grab another 2 Vibers and throw them away. I can repeat attempts and finally I will get 1 V &1 C.

Is that logic ok?

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New post 30 Jun 2017, 02:19
Mo2men wrote:
Bunuel wrote:
Official Solution:


This is a hard question that challenges test-taker's logic. It is simple once you understand it but hard if you have never solved it. If you made a mistake on this question, make sure you understand the logic so you can be armed with this new tool for the real test.

(1) Statement 1 tells us that from any two snakes from Pandora's box at least one is a viper. This does not mean that there are 2 snakes in the box or that there is only 1 viper. Instead, it indicates that at most, there is 1 cobra. This may mean 1 cobra and 1 viper or 1 cobra and 99 vipers. Make sure you understand this distinction. S1 tells us that there is only 1 cobra in the box, which is sufficient.

(2) The total number of snakes Pandora's box is 99. Clearly insufficient.


Answer: A



Dear Bunuel

I went along the thread but I could not understand something about fact 1.

If I use info in Fact 2 in Fact 1, it says 'at least 1 Viber' and throw them away. It means I can grab another 2 Vibers and throw them away. I can repeat attempts and finally I will get 1 V &1 C.

Is that logic ok?


Sorry but I cannot understand at all what you mean. Do you mean statement 1 and 2 by fact 1 and 2? What do you mean throw away?
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Re: M07-18 [#permalink]

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New post 30 Jun 2017, 02:36
Bunuel wrote:
Mo2men wrote:
Bunuel wrote:
Official Solution:


This is a hard question that challenges test-taker's logic. It is simple once you understand it but hard if you have never solved it. If you made a mistake on this question, make sure you understand the logic so you can be armed with this new tool for the real test.

(1) Statement 1 tells us that from any two snakes from Pandora's box at least one is a viper. This does not mean that there are 2 snakes in the box or that there is only 1 viper. Instead, it indicates that at most, there is 1 cobra. This may mean 1 cobra and 1 viper or 1 cobra and 99 vipers. Make sure you understand this distinction. S1 tells us that there is only 1 cobra in the box, which is sufficient.

(2) The total number of snakes Pandora's box is 99. Clearly insufficient.


Answer: A



Dear Bunuel

I went along the thread but I could not understand something about fact 1.

If I use info in Fact 2 in Fact 1, it says 'at least 1 Viber' and throw them away. It means I can grab another 2 Vibers and throw them away. I can repeat attempts and finally I will get 1 V &1 C.

Is that logic ok?


Sorry but I cannot understand at all what you mean. Do you mean statement 1 and 2 by fact 1 and 2? What do you mean throw away?



I will try to simplify what I mean.

Does Statement 1 mean that in each time in I grab ANY two snakes, those snakes MUST be 1 V and 1 C. Or Could it be 2 Vibers?

My understanding:

I used imaginary situation that I have box with 99 snakes. Each time I grab two snakes it might be (2 V) or (1 V and 1 C). Suppose we have 4 snakes in the box. I can grab first 2 as Viper and keep them aside. In the second 2 snakes MUST be 1 V and 1 C.

Suppose I have 5 snakes. I cab grab in first 2 attempts 2 V snakes and keep them aside. So the last snake MUST be Cobra.

P.S. The term 'throw away' is mean to keep them aside before doing second attempt.

I hop I was clear.

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Re: M07-18 [#permalink]

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New post 30 Jun 2017, 02:42
Mo2men wrote:

I will try to simplify what I mean.

Does Statement 1 mean that in each time in I grab ANY two snakes, those snakes MUST be 1 V and 1 C. Or Could it be 2 Vibers?

My understanding:

I used imaginary situation that I have box with 99 snakes. Each time I grab two snakes it might be (2 V) or (1 V and 1 C). Suppose we have 4 snakes in the box. I can grab first 2 as Viper and keep them aside. In the second 2 snakes MUST be 1 V and 1 C.

Suppose I have 5 snakes. I cab grab in first 2 attempts 2 V snakes and keep them aside. So the last snake MUST be Cobra.

P.S. The term 'throw away' is mean to keep them aside before doing second attempt.

I hop I was clear.


The first statement does not mean that you are taking the snakes and throwing them away. It means that out of all possible cases to pick two snakes out of the box there will be at least one viper. So, no matter which two snakes you pick you can get either two vipers or one viper and one cobra.
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Re: M07-18 [#permalink]

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New post 30 Jun 2017, 02:48
Bunuel wrote:
Mo2men wrote:

I will try to simplify what I mean.

Does Statement 1 mean that in each time in I grab ANY two snakes, those snakes MUST be 1 V and 1 C. Or Could it be 2 Vibers?

My understanding:

I used imaginary situation that I have box with 99 snakes. Each time I grab two snakes it might be (2 V) or (1 V and 1 C). Suppose we have 4 snakes in the box. I can grab first 2 as Viper and keep them aside. In the second 2 snakes MUST be 1 V and 1 C.

Suppose I have 5 snakes. I cab grab in first 2 attempts 2 V snakes and keep them aside. So the last snake MUST be Cobra.

P.S. The term 'throw away' is mean to keep them aside before doing second attempt.

I hop I was clear.


The first statement does not mean that you are taking the snakes and throwing them away. It means that out of all possible cases to pick two snakes out of the box there will be at least one viper. So, no matter which two snakes you pick you can get either two vipers or one viper and one cobra.


Thanks for your answer

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New post 02 Jul 2017, 16:15
What if there are other snakes in the box, The question doesn't mention Viper and Cobra are the only 2 kinds of snakes. For any 2 snakes, if you have a Viper, couldn't that mean {Viper, Rattle Snake} as well?

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Re: M07-18 [#permalink]

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New post 02 Jul 2017, 16:37
bhargavsrini wrote:
What if there are other snakes in the box, The question doesn't mention Viper and Cobra are the only 2 kinds of snakes. For any 2 snakes, if you have a Viper, couldn't that mean {Viper, Rattle Snake} as well?



I saw the same question answered by Bunuel in page 2 or 3.

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New post 11 Jul 2017, 14:33
josegf1987 wrote:
At least one is a Viper --> Couldn't there be two vipers - and therefore 0 cobras - and invalidate statement 1? Thanks.


Any answer to this? Wondering the same thing here!

Thanks

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josegf1987 wrote:
At least one is a Viper --> Couldn't there be two vipers - and therefore 0 cobras - and invalidate statement 1? Thanks.


In DS questions, you are never trying to 'invalidate' the statements. The statements are facts - they can't be wrong. You're trying to work out whether the question "how many cobras are there?" can have only one answer, or more than one answer.

If, when looking at one statement, you're considering a scenario that would make that statement false, you're considering a scenario that doesn't agree with the information you've been provided, so you're considering a scenario that isn't relevant to the problem.
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Is this one of your questions, Bunuel? It's a really good question - it's logically tricky, but the setup is elegantly simple, like in many real high-level GMAT problems.

In case it helps anyone, when I read Statement 1, I rephrased it this way: "if you pick two snakes from the box, you will never pick two cobras". That means there can be at most one cobra in the box, and since there's at least one, there must be exactly one.
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New post 11 Jul 2017, 15:31
IanStewart wrote:
josegf1987 wrote:
At least one is a Viper --> Couldn't there be two vipers - and therefore 0 cobras - and invalidate statement 1? Thanks.


In DS questions, you are never trying to 'invalidate' the statements. The statements are facts - they can't be wrong. You're trying to work out whether the question "how many cobras are there?" can have only one answer, or more than one answer.

If, when looking at one statement, you're considering a scenario that would make that statement false, you're considering a scenario that doesn't agree with the information you've been provided, so you're considering a scenario that isn't relevant to the problem.


Agreed not trying to invalidate statements - I was having a hard time understanding how (1) would still be sufficient in a scenario where we could have 0 cobras or 1 cobra in the box.

After giving the question another read, I see that it clearly states that "There is at least one viper and at least one cobra in Pandora's box".

It now makes sense. 8-)

Thank you

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