Data Sufficiency Q - MGMAT : GMAT Data Sufficiency (DS)
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# Data Sufficiency Q - MGMAT

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Manager
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Data Sufficiency Q - MGMAT [#permalink]

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28 Apr 2011, 05:01
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Hi folks

Please help me understand the concept. In Chapter 2 pg 40 of the guide 1 there is a Q

Is product of all the elements in Set S negative?

i) All of the elements in S are negative
ii) There are 5 negative numbers in Set S

Book explains :

i) Odd number of negatives so ans will be negative - INSUFFICIENT (understood).

ii) " Based on what we have learned so far it seems that the statement (ii) tells us that the product must be negative. However if any of the elements in Set S equals zero, then the product of the element in Set S will be zero which is NOT negative. Therefore Statement (ii) is INSUFFICIENT"

Combined SUFFICIENT.

I am unable to understand why is zero an option here. Zero is neither +ve not -ve. So how can we consider 0 as an option here?

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Re: Data Sufficiency Q - MGMAT [#permalink]

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28 Apr 2011, 05:31
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i'm not sure if I got your question right but let me give it a try. The question is asking whether the product of a set S is negative. There are three possibilities you have to consider in this question. Set S could be 0, negative or positive. You MUST consider 0 as a possibility.

You will encounter expressions in the GMAT like
$$a<0$$
That means a is negative.
$$a>0$$
That means a is positive.
$$a=0$$
That means it is zero.

There ARE always three states in a number or value. So, 0 is ALWAYS an option.

ii) There are 5 negative numbers in Set S

The test taker put this odd numbers of negative to make us think that the product is negative. But that is a trap. Unless, it is stated that there is NO zero element OR there are no other elements. Then we are certain, it's negative. Hence Insufficient.

melguy wrote:
Hi folks

Please help me understand the concept. In Chapter 2 pg 40 of the guide 1 there is a Q

Is product of all the elements in Set S negative?

i) All of the elements in S are negative
ii) There are 5 negative numbers in Set S

Book explains :

i) Odd number of negatives so ans will be negative - INSUFFICIENT (understood).

ii) " Based on what we have learned so far it seems that the statement (ii) tells us that the product must be negative. However if any of the elements in Set S equals zero, then the product of the element in Set S will be zero which is NOT negative. Therefore Statement (ii) is INSUFFICIENT"

Combined SUFFICIENT.

I am unable to understand why is zero an option here. Zero is neither +ve not -ve. So how can we consider 0 as an option here?

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Re: Data Sufficiency Q - MGMAT [#permalink]

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28 Apr 2011, 06:42
melguy wrote:
Hi folks

Please help me understand the concept. In Chapter 2 pg 40 of the guide 1 there is a Q

Is product of all the elements in Set S negative?

i) All of the elements in S are negative
ii) There are 5 negative numbers in Set S

Book explains :

i) Odd number of negatives so ans will be negative - INSUFFICIENT (understood).

ii) " Based on what we have learned so far it seems that the statement (ii) tells us that the product must be negative. However if any of the elements in Set S equals zero, then the product of the element in Set S will be zero which is NOT negative. Therefore Statement (ii) is INSUFFICIENT"

Combined SUFFICIENT.

I am unable to understand why is zero an option here. Zero is neither +ve not -ve. So how can we consider 0 as an option here?

I think II confuses you in that the statement only says that "there are 5 negative number in the set" but not says "there are 5 numbers and all these numbers are negative". So there is no information about other numbers. Therefore, completely there can be a Zero in "that other numbers". In that sense, product of all elements in set S can be 0 and negative. You do not know it is 0 or negative. It is not sufficient to answer the question. right?

However, I and II combined, you know exactly that set S has only 5 numbers and all of these 5 are negative. Sufficient

Hope it helps
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Re: Data Sufficiency Q - MGMAT [#permalink]

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28 Apr 2011, 19:50
Straight C as we don't know whether the element in the set has a zero in case of B.
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Re: Data Sufficiency Q - MGMAT   [#permalink] 28 Apr 2011, 19:50
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