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M07-18

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Bunuel
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M07-18 [#permalink] New post   16 Sep 2014, 00:35
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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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Bunuel
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Re M07-18 [#permalink] New post   16 Sep 2014, 00:35
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Official Solution:


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

This question is challenging and requires logical reasoning. Once you understand the logic behind it, the question becomes simple. However, if you have never encountered this type of problem before, it can be difficult to solve. If you made an error, it's important to review the solution and understand the reasoning, as it can be a valuable tool for similar problems on actual test.

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

Statement (1) states that from ANY two snakes in the box, at least one is a viper. This means that there cannot be two or more cobras in the box, because if there were, then we could choose two cobras and that would contradict the statement. Therefore, there must be at most one cobra in the box. And since we also know that there is at least one cobra in the box, there must be exactly one cobra. So, statement (1) is sufficient to answer the question.

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


Answer: A
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sasha40612
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Re: M07-18 [#permalink] New post   16 Mar 2015, 04:58
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this is a good question.

To people who are still confused about the 1st statement the below example should help you.

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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Princas1
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Re: M07-18 [#permalink] New post   24 Nov 2014, 09:34
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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

Please explain

Thank you
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Bunuel
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Re: M07-18 [#permalink] New post   24 Nov 2014, 09:42
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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

Please explain

Thank you


Let me ask you if there are 5 vipers and 5 cobras, would the second statement be correct?
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Re: M07-18 [#permalink] New post   24 Nov 2014, 10:17
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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.
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Re: M07-18 [#permalink] New post   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

Please explain

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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Re: M07-18 [#permalink] New post   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

Please explain

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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Re: M07-18 [#permalink] New post   27 May 2015, 16:34
At least one is a Viper --> Couldn't there be two vipers - and therefore 0 cobras - and invalidate statement 1? Thanks.
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Re: M07-18 [#permalink] New post   31 Oct 2015, 14:32
I think this is a high-quality question and I agree with explanation.
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Re: M07-18 [#permalink] New post   12 Jul 2016, 08:03
I think this is a high-quality question and I agree with explanation.
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Re: M07-18 [#permalink] New post   20 Jul 2016, 22:32
I think this is a high-quality question and I agree with explanation.
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Re: M07-18 [#permalink] New post   11 Jan 2017, 11:52
I think this is a high-quality question and I agree with explanation.
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Re: M07-18 [#permalink] 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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Re: M07-18 [#permalink] New post   29 Jun 2017, 04:34
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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] New post   11 Jul 2017, 15:04
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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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Re: M07-18 [#permalink] New post   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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Re: M07-18 [#permalink] New post   11 Jul 2017, 22:24
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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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Re: M07-18 [#permalink] New post   25 Dec 2017, 02:56
I think this is a high-quality question and I agree with explanation.
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Re: M07-18 [#permalink] New post   25 Feb 2018, 20:54
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