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# M07-18

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Intern
Joined: 04 Mar 2019
Posts: 4

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08 Apr 2019, 18:31
alikm wrote:
why are we assuming that there is only 2 types of snakes in the box?

There is no need to assume that there are only 2 types of snakes while reading the main statement. However when you apply the first condition, the assumption of more than 2 types of snakes is eliminated. Because if there were 3 types of snakes there is no way to ensure that there is 1 viper among the 2 snakes are selected.

A thing to keep in mind is that the question isn't asking to determine whether there will be 1 viper among the 2 snakes selected. It is a condition applied to the main statement.
Intern
Joined: 24 Dec 2018
Posts: 4

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24 Apr 2019, 09:47
This is more of a puzzle than a Quant problem, but its good to know what the wordings imply:
"From any two snakes from Pandora's box at least one is a viper"
Implies for any combination of two snakes we can never have two Cobras. This can only happen if there is 1 cobra.
Intern
Joined: 09 Mar 2019
Posts: 11

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10 Jul 2019, 02:29
You can look at this if there are X snakes in Pandora's Box and as per statement 1 if you take out any two snakes out of X there can be at least 1 viper.

Now what does that mean : That mean you can have 1 viper and 1 cobra or 2 vipers in any two pairs chosen from Pandora's Box.
That means there cant be two cobras in any pair chosen. That will violate the statement one. and as per question stem there is at least one cobra that confirms that there can be at most one cobra only.
Manager
Joined: 09 Apr 2017
Posts: 80
GPA: 3.99

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27 Jul 2019, 09:34
Analysis: (I got this wrong, i read the previous posts and answers, re-illustrated and now I finally understood. Thanks for this wonderful Tricky question)

Question stem says, at least one cobra and one viper

Stmt 1 says,
At least one viper when you pick ANY two snakes

So the Combination of two snakes are :
VV - OK
VC - OK
CV - OK
CC - This is not possible, since there must be at least one Viper in a pair of snakes

=====================================================================

Case 1:
V V V V V V
V V C V V V
V V V V V V
In case 1, I could get only the following combinations
VV - OK
VC - OK
CV - OK
(Therefore, this is exactly what was mentioned in the question stem and statement 1)

Case 2:
V V V V V V
V C C V V V
V V V V V V
In case 2, I could get all the following combinations
VV - OK
VC - OK
CV - OK
CC - This is not possible, since there must be at least one Viper in a pair of snakes
(Therefore, this is NOT what was mentioned in the question stem and statement 1)

YOU CAN HAVE ONLY one COBRA as in CASE 1

=====================================================================

in statement 2, the total snakes are 99.
So i could have any combinations of snakes As long as at least one cobra and at least one viper as mentioned in the question stem

98C + 1V
91C + 8V

So, statement 2 is not useful at all.
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03 Aug 2019, 22:15
I honestly don't think many people got this right. A lot of the responses in this thread are merely justifications.
Intern
Joined: 04 Jun 2019
Posts: 10

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15 Oct 2019, 07:06
hello Bunnel,

Can you please suggest some similar questions to practice based on above concept.
Intern
Joined: 09 Sep 2013
Posts: 3

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23 Oct 2019, 03:18
I think this is a poor-quality question and the explanation isn't clear enough, please elaborate. hi,
according to 1, there is at least one viper in "any" pair of snakes taken from the box. so lets aasume that there are 40 pairs:
vv
vc
vc
vc
vv
.
.
.
.
so we can not calculate the number of cobras exactly from what is given in 1.
could you please tell me where I am wrong,
thanks
Math Expert
Joined: 02 Sep 2009
Posts: 59674

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23 Oct 2019, 03:22
Voyagegrande wrote:
I think this is a poor-quality question and the explanation isn't clear enough, please elaborate. hi,
according to 1, there is at least one viper in "any" pair of snakes taken from the box. so lets aasume that there are 40 pairs:
vv
vc
vc
vc
vv
.
.
.
.
so we can not calculate the number of cobras exactly from what is given in 1.
could you please tell me where I am wrong,
thanks

This is explained several times on previous pages. I suggest you to re-read the solution more carefully and if this does not helps, read the whole discussion. This is one of the hardest questions in the test but I assure you that it's 100% correct.
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Joined: 12 Sep 2015
Posts: 4134

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28 Nov 2019, 08:03
Top Contributor
Bunuel wrote:
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.

Given: There is at least one viper and at least one cobra in Pandora's box.

Target question: How many cobras are there?

Statement 1: From any two snakes from Pandora's box at least one is a viper.
This tells us that there CANNOT be more than one cobra in the box.
For example, if there were TWO cobras and the box, then it's possible to have two snakes (both cobras) such that neither is a viper, which would break the condition that at least one snake must be a viper.
Since we are told there is at least one cobra, and since we have now concluded that there CANNOT be more than one cobra in the box, the answer to the target question is there is exactly 1 cobra in the box
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: The total number of snakes in Pandora's box is 99
There are many scenarios that satisfy statement 2. Here are two:
Case a: There are 10 cobras and 89 vipers. In this case, the answer to the target question is there are 10 cobras in the box
Case b: There are 11 cobras and 88 vipers. In this case, the answer to the target question is there are 11 cobras in the box
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Cheers,
Brent
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Re: M07-18   [#permalink] 28 Nov 2019, 08:03

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# M07-18

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