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M07-18

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16 Sep 2014, 00:35
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65% (hard)

Question Stats:

44% (01:00) correct 56% (01:13) wrong based on 377 sessions

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There is at least one viper and at least one cobra in Pandora's box. How many cobras are there?

(1) From any two snakes from Pandora's box at least one is a viper.

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

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16 Sep 2014, 00:35
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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.

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24 Nov 2014, 10:17
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5
It took me sometime to understand statement 1 in the test. For those having trouble like me, hope this helps!
Statement 1: Any 2 snakes, possibilities ---> V, V or V, C or C, V.
There is no possibility for C, C. This means that there is only 1 cobra in the box. Sufficient.

Statement 2: Totally irrelevant and useless.
General Discussion
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26 Dec 2014, 07:59
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TudorM wrote:
Bunuel wrote:
Princas1 wrote:
Yes but we do know know how many snakes there are in the box.

For example if the number of snakes is 10 there could be 9 ; 1 or it could be 5;5.

Second one is clearly insufficient also

And both are insufficient.

99 Snakes 1 cobra 98 vipers, or 97/2

Thank you

Let me ask you if there are 5 vipers and 5 cobras, would the second statement be correct?

Hey Bunuel, it's still not clear for me concerning answer (1).

If we take your example with 10 snakes, doesn't it mean that we can have anything from (5V 5C; 6V 4C;...9V 1C) according to statement 1? A ratio of 6:4 V to C is still "at least 1 viper" for any 2 snakes.

Thanks for clarifying.

NO. We cannot have more than 1 cobras. If there are 5 cobras and 5 vipers then the first statement will NOT hold. (1) says from ANY two snakes from Pandora's box at least one is a viper. If there are 5 cobras and 5 vipers then we could have two snakes from which BOTH are vipers.
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16 Mar 2015, 04:58
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this is a good question.

Ex:

Stated in the question
There is at least one viper and at least one cobra in Pandora's box

Statement 1
From any two snakes from Pandora's box at least one is a viper.

Cases that are in scope and are correct are
1V 1C is correct
2V 1C is correct
3V 1C is correct
.
.
.
n-1V 1C is correct
where n >0 and n is an integer

Here the no of cobras are always one because in the question it is stated that there is at least one cobra in Pandora's box. So minimum value of no of cobras is 1

Note:
Cases that are out of scope.
1V 2C
2V 2C
3V 3C etc...

Notice the no of cobras is always greater one . But what does the statement 1 say "from any two snakes at least one is a viper."
So all the above cases are out of scope as there is a chance that from any two snakes none can be a viper.

Hope this helps.
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20 Jan 2015, 20:57
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i see the goal here (trickery), but the question wording is wrong.

Implication of "any" two snakes is that there are more than 1 pair, otherwise proper english would be "the" two snakes.

This one should be dumped from the question bank.
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11 Jul 2017, 15:15
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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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10 Nov 2014, 02:58
1
shyam593 wrote:
Bunuel wrote:
Official Solution:

(1) From any two snakes from Pandora's box at least one is a viper. Since from ANY two snakes one is a viper then there cannot be 2 (or more) cobras and since there is at least one cobra then there must be exactly one cobra in the box. Sufficient.

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

Hi

From any two snakes from Pandora's box at least one is a viper
does not it mean that if 2 snakes were taken out from the box at least one is viper
if you consider this will the answer be different

Yes, it means exactly that. But what do you mean that the answer would be different?
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10 Nov 2014, 03:14
1
Bunuel wrote:
shyam593 wrote:
Bunuel wrote:
Official Solution:

(1) From any two snakes from Pandora's box at least one is a viper. Since from ANY two snakes one is a viper then there cannot be 2 (or more) cobras and since there is at least one cobra then there must be exactly one cobra in the box. Sufficient.

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

Hi

From any two snakes from Pandora's box at least one is a viper
does not it mean that if 2 snakes were taken out from the box at least one is viper
if you consider this will the answer be different

Yes, it means exactly that. But what do you mean that the answer would be different?

Sorry got it now
irrespective of the no of vipers, cobra can never be more than 1.
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24 Nov 2014, 09:42
1
Princas1 wrote:
Yes but we do know know how many snakes there are in the box.

For example if the number of snakes is 10 there could be 9 ; 1 or it could be 5;5.

Second one is clearly insufficient also

And both are insufficient.

99 Snakes 1 cobra 98 vipers, or 97/2

Thank you

Let me ask you if there are 5 vipers and 5 cobras, would the second statement be correct?
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23 Sep 2015, 12:22
1
I think this is a poor-quality question and the explanation isn't clear enough, please elaborate.
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17 Feb 2016, 12:13
1
1
A lot of people on this forum are over-complicating things.

If you grab ANY TWO snakes, one or more has to be a viper. That is saying that it's IMPOSSIBLE to grab 2 cobras. So there is only 1 cobra as per the question stem.
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09 Jul 2016, 09:12
1
expertesp wrote:
I think this is a poor-quality question and I don't agree with the explanation. Hi there, so for (1) in my opinion let us assume it is 2 snakes only in the box. it could be 1 cobra and 1 viper or 2 vipers and 0 cobras. two potential solutions. Or do you say because of the first sentence *there is atl east one viper and at least one cobra in the box* this tells us the other one must for sure be a cobra?

The question is correct. It's not just that easy.

As for your question: the stem clearly says in the first sentence "There is at least one viper and at least one cobra in Pandora's box". WHY do you consider the case which contradicts this???
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25 May 2017, 00:49
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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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11 Jul 2017, 15:04
1
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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11 Jul 2017, 22:24
1
1
IanStewart wrote:
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.

Yes, this is one of my questions. I knew that it would be a hard question when writing it but it turned out to be one of the hardest ones based on the timer stats and replies.

The same way a simple principle tested here: https://gmatclub.com/forum/m03-183621.html#p1413892 seems to be hard to grasp for many.
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15 Oct 2014, 12:04
1
Bunuel wrote:
Official Solution:

(1) From any two snakes from Pandora's box at least one is a viper. Since from ANY two snakes one is a viper then there cannot be 2 (or more) cobras and since there is at least one cobra then there must be exactly one cobra in the box. Sufficient.

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

Hi Bunuel,
Any specific types/patterns of word problems that you could suggest here.

Facing a lot of time issues especially when these word problems come in DS mode.
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09 Nov 2014, 16:26
Bunuel wrote:
Official Solution:

(1) From any two snakes from Pandora's box at least one is a viper. Since from ANY two snakes one is a viper then there cannot be 2 (or more) cobras and since there is at least one cobra then there must be exactly one cobra in the box. Sufficient.

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

Hi

From any two snakes from Pandora's box at least one is a viper
does not it mean that if 2 snakes were taken out from the box at least one is viper
if you consider this will the answer be different
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24 Nov 2014, 09:34
Yes but we do know know how many snakes there are in the box.

For example if the number of snakes is 10 there could be 9 ; 1 or it could be 5;5.

Second one is clearly insufficient also

And both are insufficient.

99 Snakes 1 cobra 98 vipers, or 97/2

Thank you
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26 Dec 2014, 00:35
Bunuel wrote:
Princas1 wrote:
Yes but we do know know how many snakes there are in the box.

For example if the number of snakes is 10 there could be 9 ; 1 or it could be 5;5.

Second one is clearly insufficient also

And both are insufficient.

99 Snakes 1 cobra 98 vipers, or 97/2

Thank you

Let me ask you if there are 5 vipers and 5 cobras, would the second statement be correct?

Hey Bunuel, it's still not clear for me concerning answer (1).

If we take your example with 10 snakes, doesn't it mean that we can have anything from (5V 5C; 6V 4C;...9V 1C) according to statement 1? A ratio of 6:4 V to C is still "at least 1 viper" for any 2 snakes.

Thanks for clarifying.
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