Weaken CR - Hard - Expert explanation please. - The Beat The GMAT Forum

Weaken CR - Hard - Expert explanation please.

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GMATMadeEasy: Legendary Member; Posts: 768; Joined: Mon Nov 30, 2009 3:46 amFollowed by: 7 members; Thanked: 21 times

by GMATMadeEasy » Sun Nov 07, 2010 3:14 pm

The average age of chief executive officers (CEO's) in a large sample of companies is 57. The average age of CEO's in those same companies 20 years ago was approximately eight years younger. On the basis of those data, it can be concluded that CEO's in general tend to be older now.
Which of the following casts the most doubt on the conclusion drawn above?
(A) The dates when the CEO's assumed their current positions have not been specified.
(B) No information is given concerning the average number of years that CEO's remain in office.
(C) The information is based only on companies that have been operating for at least 20 years.
(D) Only approximate information is given concerning the average age of the CEO's 20 years ago.
(E) Information concerning the exact number of companies in the sample has not been given.

OA is C
Could someone explain why A is not correct answer ? I rather find B is also weaking the argument?

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Source: Beat The GMAT — Critical Reasoning | Sun Nov 07, 2010 3:14 pm

rkanthilal: Master | Next Rank: 500 Posts; Posts: 154; Joined: Thu Aug 26, 2010 9:32 amFollowed by: 19 members; Location: Chicago,IL; Thanked: 46 times; GMAT Score:760

by rkanthilal » Sun Nov 07, 2010 3:59 pm

I'm not a CR expert but here are my thoughts on this.

P1: The average age of chief executive officers (CEO's) in a large sample of companies is 57.
P2: The average age of CEO's in those same companies 20 years ago was approximately eight years younger.
C1: On the basis of those data, it can be concluded that CEO's in general tend to be older now.

(A) The dates when the CEO's assumed their current positions have not been specified. Incorrect. This is irrelevant. The conclusion is that CEO's in general tend to be older now. When they assumed their position does not matter.

(B) No information is given concerning the average number of years that CEO's remain in office. Incorrect. Similar to (A), this is also irrelevant. The conclusion is that CEO's in general tend to be older now. How long they have been in their position does not matter.

(C) The information is based only on companies that have been operating for at least 20 years. Correct. The argument refers to a sample of companies that have CEOs with an average age of 57. Twenty years ago, these same companies had CEO's that were on average 8 years younger. The conclusion is made about CEO's "in general". This conclusion is too broad based on the evidence provided. If you were to consider the age of CEO's in companies that have not been around for 20 years the conclusion may not hold.

(D) Only approximate information is given concerning the average age of the CEO's 20 years ago. Incorrect. The conclusion is that CEO's today are on average older than CEO's 20 years ago. The information on how much older they are doesn't need to be exact in order for the conclusion to hold. As long as they are older the conclusion holds.

(E) Information concerning the exact number of companies in the sample has not been given. Incorrect. This answer choice attacks the sample of companies referenced in the argument. There is a sampling error, but this is not it. The argument mentions that a "large" number of companies was sampled. The exact number is irrelevant. The error is in the members of the sample (only companies that have been around for 20 years) and not the number of companies sampled.

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GMATMadeEasy: Legendary Member; Posts: 768; Joined: Mon Nov 30, 2009 3:46 amFollowed by: 7 members; Thanked: 21 times

by GMATMadeEasy » Thu Nov 11, 2010 12:46 pm

@rkanthilal : You have got an excellent hold on CR. Very good explanations.

For C I agree that it is fine.

For A and B, dont you think if these are the same CEOs, then this obviouslsy gives the wrong results ?

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rkanthilal: Master | Next Rank: 500 Posts; Posts: 154; Joined: Thu Aug 26, 2010 9:32 amFollowed by: 19 members; Location: Chicago,IL; Thanked: 46 times; GMAT Score:760

by rkanthilal » Thu Nov 11, 2010 2:50 pm

GMATMadeEasy wrote:@rkanthilal : You have got an excellent hold on CR. Very good explanations.

For C I agree that it is fine.

For A and B, dont you think if these are the same CEOs, then this obviouslsy gives the wrong results ?

Thanks for your nice words...

The argument claims that the age of CEO's today is greater than the age of CEO's 20 years ago. The argument is not concerned about who the CEO's are. The fact that some of them may be the same people that were surveyed 20 years ago does not affect the conclusion.

I think the problem you are having with this is that you are looking for an error in the wrong place. The mistake that this survey makes is that it only counts CEO's in companies that are likely to have older CEO's (companies that have been around for more than 20 years). Who the CEO's are is irrelevant. The fact that they are CEO qualifies them to be counted in this survey. This is not the problem. The problem is that the survey should include a broader sample of companies that are more representative of the general economy. In other words, the survey is biased.

Hope this helps...

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