I'm Doubting the Official Answer of a CR question

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Dear all,

Below Critical reasoning question from GMAT REVIEW 13th edition:

Question # 87:

In the United States, of the people who moved from one state to another when they retired, the percentage who retired to Florida has decreased by three percentage points over the past ten years. Since many local businesses in Florida cater to retirees, these declines are likely to have a noticeably negative economic effect on these businesses and therefore on the economy of Florida.

Which of the following, if true, most seriously weakens the argument given?

(A) People who moved from one state to another when they retired moved a greater distance, on average, last year than such people did ten years ago.
(B) People were more likely to retire to North Carolina from another state last year than people were ten years ago.
(C) The number of people who moved from one state to another when they retired has increased significantly over the past ten years.
(D) The number of people who left Florida when they retired to live in another state was greater last year than it was ten years ago.
(E) Florida attracts more people who move from one state to another when they retire than does any other state.

The OA is C.

The conclusion that the argument makes is that the business and economy of florida will be negatively effected because of the decline in retirees in Florida (while noting the premise that Florida's economy and businesses strongly rely on retirees).

In consideration of the above, how can C weaken the argument? Even if the number of retirees moving from one state to another has increased over the past 10 years (as OA C suggests), it doesn't mean that such increase is accompanied by a corresponding increase in the number of retirees in florida... It could be the case that the number of retirees in other states increased considerably which had offset a corresponding decrease in retirees in florida.

PLease let me know what you guys think.

THanks and BR,
MJ.

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by The Iceman » Sun Jan 06, 2013 5:09 am
mjabki wrote: In consideration of the above, how can C weaken the argument? Even if the number of retirees moving from one state to another has increased over the past 10 years (as OA C suggests), it doesn't mean that such increase is accompanied by a corresponding increase in the number of retirees in florida... It could be the case that the number of retirees in other states increased considerably which had offset a corresponding decrease in retirees in florida.

PLease let me know what you guys think.

THanks and BR,
MJ.
First, official answers are not to be doubted, simply because they are always correct :). This understanding will also help you a lot in learning why right answers are right and make your life easier during the prep.

We need to weaken the conclusion "these declines are likely to have a noticeably negative economic effect on these businesses and therefore on the economy of Florida"

C says "the number of people who moved from one state to another when they retired has increased significantly over the past ten years"

let us say the # of retirees increases from 100 to 100,000. And even if the share of retirees going to Florida decreases from 15% to 12%, the number of retirees going to Florida changes from 15 to 12,000.

This clearly weakens the conclusion because there is no decline in the number of retirees in the first place!

Now, coming to your point. Please remember that you do not need to 100% destroy the conclusion in weaken/strengthen problems. Instead even a mild weakening/strengthening is enough for the statement to be a weakener/strenghener.

Notice the word significantly in statement C. It gives a good idea that the number of migrating retirees has increased by leaps and bounds. There is a strong likelihood that a 3% drop in the share for Florida will not be able to offset or even come any where close to causing an actual decline in the absolute numbers for Florida. This is enough for the statement to weaken the argument.

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by mjabki » Sun Jan 06, 2013 8:48 am
Bingo- got it.

Thanks alot.

BR,
MJ.

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by ceilidh.erickson » Thu Jan 10, 2013 7:42 am
I think Vineet's explanation is a very good one. I just want to add a general bit of advice:

Many of the CR arguments that rely on logical gaps (assumptions, evaluate, strengthen, and weaken questions) test the logical gap between PROPORTIONS and REAL NUMBERS. If the premises give information about a percent, proportion, or ratio, and the argument concludes something about actual numbers, there is an assumption that the actual numbers have not changed.

Consider this hypothetical argument: The percentage of applicants accepted into business schools was higher this year than in any year previous. Therefore, business schools must be admitting larger classes than ever before.

Here, we have a logical gap - we don't know if the number of applicants was the same this year as last year.

So be on the lookout for the language of PROPORTION - percent, ratio, fraction, etc - and then ask yourself, "what do I know about actual NUMBERS?"

In question #87, we're given a percent change: the percentage of retirees decreased by 3 points. But what is that a percent chance from? It's not that Florida retirees are 3% lower than Florida retirees 10 years ago. It's that as a percent of all retirees, the percent retiring to Florida has decreased. So, Florida has a slightly smaller piece of the whole country's retirement pie (if you think in terms of a pie chart). But what if the pie itself is much bigger this year? A smaller percentage of a larger pie would be more people overall.
Ceilidh Erickson
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Harvard Graduate School of Education

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by lunarpower » Sat Jan 12, 2013 10:40 pm
what ceilidh said.

more generally, if you see ANY substitution of one statistic for another, then you should immediately start thinking about any differences/discrepancies that might exist between those statistics.
you don't need to memorize anything here -- these are all going to be statistics with which you've been familiar for a long, long time -- but, just be aware: if the argument suddenly shifts from one type of statistic to another, they want you to pay attention!

just a couple of examples (not an exhaustive list -- just the first couple that come to mind)

* aggregate statistics vs. per-capita statistics
(e.g., the total number of murders in a city vs. the total number of murders per 100,000 people in that city -- the size of the city would affect the former, but not the latter)

* aggregate statistics vs. statistics "per" anything at all
(e.g., the total amount of waste generated by a factory vs. the total waste per worker generated by the factory -- the latter, but not the former, would be affected by changes in the number of workers)

* absolute numbers vs. percentages
(as ceilidh pointed out)

* overall trends vs. individual data points (e.g., if we know that industry X suffered losses last year, and firm Y is in industry X, that doesn't mean firm Y necessarily suffered losses last year)

... and so on.
basically, if the measure used in the conclusion is not exactly the same as the measure(s) used in the argument, you should examine that aspect of the argument very closely.
Ron has been teaching various standardized tests for 20 years.

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by VIGNESHWARR » Thu Jun 27, 2013 9:57 am
Why not the option E.Please explain

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by lunarpower » Thu Jun 27, 2013 6:46 pm
VIGNESHWARR wrote:Why not the option E.Please explain
the argument is concerned solely with the situation in florida, so any comparison to another state is irrelevant.

as an analogy, if you are gaining weight and trying to figure out why, then anything like "well, my brother is gaining weight even faster than i am!" or "i still don't weigh as much as my brother!" is obviously irrelevant. the key is to take that same intuition -- the intuition that (hopefully) makes it obvious that these things are irrelevant -- and apply it to the problem that you see here.
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