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Tough DS

by rakeshd347 » Thu Oct 17, 2013 9:08 pm
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 Pandora's box is 99.
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by theCodeToGMAT » Thu Oct 17, 2013 9:18 pm
V >= 1
C >= 1

To find: C?

Statement 1:
This means that there is only ONE other SNAKE except VIPER.. and its clear in question that there is atleast one COBRA..So, COBRA = 1
SUFFICIENT

Statement 2:
V+C = 99
INSUFFICIENT


is it {A}?
Last edited by theCodeToGMAT on Thu Oct 17, 2013 10:10 pm, edited 1 time in total.
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by vipulgoyal » Thu Oct 17, 2013 9:55 pm
Probablity of Viper cant be 1 because in box there is at least 1 viper and one C,Is OA A ???
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by theCodeToGMAT » Thu Oct 17, 2013 10:08 pm
vipulgoyal wrote:Probablity of Viper cant be 1 because in box there is at least 1 viper and one C,Is OA A ???
Vipul what if there were say total 10 snakes and

DRAW 1: VV
DRAW 2: VC
DRAW 3: VC
DRAW 4: VV
DRAW 5: VC

Yes, I agree that Answer must be {A} but not because of the reason you sighted.

The condition Stated in Statement 1 means that there is only ONE OTHER SNAKE..and that's COBRA
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by vipulgoyal » Thu Oct 17, 2013 10:49 pm
I didnt gave ne explaination before,by saying so I contradicted the ans, you initially stated as "E before
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by theCodeToGMAT » Thu Oct 17, 2013 10:53 pm
vipulgoyal wrote:I didnt gave ne explaination before, I think you initially stated E as ans ??
I commented on your comment that "Probability can't be 1".. it can definitely be.

Yes, initially I had misunderstood the question, assuming that it meant withdrawal. That's why I considered the Probability; but the question is, infact, much direct.
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by rakeshd347 » Thu Oct 17, 2013 10:53 pm
A is the OA guys.
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by [email protected] » Thu Oct 17, 2013 10:57 pm
Hi All,

It seems as though everyone has gotten the correct answer, but since the explanations that have been offered are a bit "lean", here is why the answer is A:

We're told there's at least 1 viper and at least 1 cobra in the box. The question asks for the number of cobras.

Fact 1: If you pick any 2 snakes, you'll get AT LEAST 1 viper.

So, if you were grabbing snakes one at a time, according to Fact 1, you COULD GET:
VC
CV
VV

You COULD NOT GET:
CC

The only way to guarantee that you won't get CC is if there was ONLY ONE COBRA.
Fact 1 is SUFFICIENT

Fact 2: Total number of snakes = 99
There's not enough info to determine how many of the 99 are cobras.
Fact 2 is INSUFFICIENT.

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by vipulgoyal » Thu Oct 17, 2013 11:18 pm
Hi Rahul, I still agree that P cant be 1, suppose VVVC. in two picks 2 viper 3/4*2/3 = 1/2, in two picks one V and 1 C = 3/4 * 1/3 * 2 = 1/2 , you may take ne numbers of Vipers untill we have one C we cant have P = 1,
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by theCodeToGMAT » Thu Oct 17, 2013 11:24 pm
vipulgoyal wrote:Hi Rahul, I still agree that P cant be 1, suppose VVVC. in two picks 2 viper 3/4*2/3 = 1/2, in two picks one V and 1 C = 3/4 * 1/3 * 2 = 1/2 , you may take ne numbers of Vipers untill we have one C we cant have P = 1,
Hello Vipul, I guess we are trying to refer probability in different context :) ..

Yes the context which you are referring.. we will never have probability as "1".
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by sanju09 » Fri Oct 18, 2013 12:12 am
rakeshd347 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 Pandora's box is 99.
(1) This statement guarantees that there's only one cobra in the box. Had it not been the case, then we could not have witnessed :
From any two snakes from Pandora's box at least one is a viper
: happening. This alone is sufficient.

(2) From the total of the two positive integers, in which one has to be at least 1, we cannot take out the exact value of one of the two positive integers. This alone is hence [spoiler]insufficient.

Hence (A) is the correct answer.[/spoiler]
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by sanju09 » Fri Oct 18, 2013 12:22 am
vipulgoyal wrote:Hi Rahul, I still agree that P cant be 1, suppose VVVC. in two picks 2 viper 3/4*2/3 = 1/2, in two picks one V and 1 C = 3/4 * 1/3 * 2 = 1/2 , you may take ne numbers of Vipers untill we have one C we cant have P = 1,
What PROBABILITY serves here?
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by theCodeToGMAT » Fri Oct 18, 2013 12:25 am
sanju09 wrote:
vipulgoyal wrote:Hi Rahul, I still agree that P cant be 1, suppose VVVC. in two picks 2 viper 3/4*2/3 = 1/2, in two picks one V and 1 C = 3/4 * 1/3 * 2 = 1/2 , you may take ne numbers of Vipers untill we have one C we cant have P = 1,
What PROBABILITY serves here?[/quote

Nothing Sanjeev :) .. Was just trying to look question from different prospective.

Thanks!
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by Brent@GMATPrepNow » Thu Nov 28, 2019 6:46 am
rakeshd347 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 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

Answer: A

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Brent
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