In the nation of Pelmenia, 20% of 18-year-olds are left-handed, while

Question

In the nation of Pelmenia, 20% of 18-year-olds are left-handed, while just 10% of 45-year-olds and 2% of 70-year-olds are left-handed. But the percentage of children born left-handed has never changed in Pelmenia, nor have societal attitudes toward left-handedness.
 
Which of the following, if true, most helps to explain the variation in left-handedness among Pelmenians?

A) The number of children born each year in Pelmenia has steadily increased over the past seventy years.
 
B) In Pelmenia, left-handers are no more likely to perish in accidents than right-handers.
 
C) In Pelmenia, ambidexterity is not considered a desirable attribute.
 
D) In Pelmenia, women have a significantly lower life expectancy than men, and women are also more likely to be born left-handed.
 
E) As Pelmenians age, they become less likely to participate in surveys regarding handedness or hand dominance.

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GMATNinja · Accepted Answer

We are asked to select an answer choice that, if true, most helps to explain the variation in left-handedness among Pelmenians. Before we analyze the answer choices, let's make sure we have a clear understanding of the variation that we need to explain:

"In the nation of Pelmenia, 20% of 18-year-olds are left-handed, while just 10% of 45-year-olds and 2% of 70-year-olds are left-handed." - So the percentage of Pelmenians who are left-handed seems to vary with age. Of course, it is certainly  possible  that the percentage fluctuates in between the three given ages, but, based on the data given in the passage, it seems as though the percentage goes down as age goes up. 
 "The percentage of children born left-handed has never changed in Pelmenia." - One possible explanation for the variation is that the percentage of Pelmenian children born left-handed has steadily increased over the course of the past 70 years. This statement eliminates that possibility, so we need another explanation. 
 "Societal attitudes toward left-handedness" have never changed in Pelmenia. - Another possible explanation for the variation is that societal attitudes toward left-handedness have changed over the course of the past 70 years. For example, 70 years ago, left-handed Pelmenian children may have been viewed unfavorably and thus may have been treated in ways that decreased their odds of leading healthy and successful lives. But the information given in the passage eliminates this possible explanation.

So we need to explain why the percentage of Pelmenians who are left-handed seems to decrease with age, despite no change in the percentage of children who are born left-handed or in attitudes toward left-handedness:

We are trying to explain a variation in the PERCENTAGE of Pelmenians who are left-handed. If the number of children born each year has steadily increased, we would still expect the PERCENTAGE of left-handed children to remain the same each year. Thus, we still need something to explain why the percentage of Pelmenians who are left-handed decreases as age increases. Choice (A) does not explain the variation and can be eliminated.

A possible explanation for the variation is that left-handers ARE more likely to perish in accidents than right-handers. This would explain why the percentage of Pelmenians who are left-handed decreases as age increases. However, choice (B) tells us that left-handers are NO more likely to perish in accidents than right-handers, eliminating this possible explanation. Thus, choice (B) does not explain the variation and can be eliminated.

Choice (C) addresses another possible explanation for the variation. If ambidexterity WERE considered a desirable attribute, perhaps many left-handed Pelmenians would gradually learn to become ambidextrous over the course of their lives. This could  potentially  lead to a gradual decrease with age in the percentage of Pelmenians who are considered left-handed (once they learn to use both hands equally well, they would be considered "ambidextrous" and not "left-handed"). Choice (C) eliminates this possible explanation and does not provide an alternative, so we can get rid of (C).

Now we are on to something. If women are more likely to be born left-handed, then we can assume that the majority of left-handed Pelmenian children are female. If women and men had the same life-expectancy, we would expect the percentage of Pelmenians who are left-handed to remain the same as age increases. However, if women were more likely to die at a younger age, we would expect the percentage of Pelmenians who are left-handed to DECREASE as age increases.

In other words, if you are left-handed, you are probably a woman. Women, on average, die younger than men. Thus, on average, right-handers are likely to live longer than left-handers. This would explain the variation described in the passage, so hang on to (D).

If choice (E) said that LEFT-HANDED Pelmenians become less likely to participate in such surveys as they age, then we would have a possible explanation for the variation described in the passage. However, as written, choice (E) does not explain why the percentage decreases with age. Even if a smaller portion of Pelmenians respond to such surveys as they age, we would still expect the ratio of left-handers to right-handers to remain about the same. Choice (E) does not explain the variation and can be eliminated.

Choice (D) is the best answer.

Heisenberg12 · Answer

I was confused between D and E, but I would go with D here.

A. we have been given that the percentage of children born left-handed has remained the same. if the number of children increases, that would result in increase in number of left-handed children, however it would not explain the variation.

B. This does not help the argument. It would have made sense if the likelihood of both these events would have been unbalanced.

C. This is irrelevant to the argument at hand.

D. Correct. This explains why there is a variation in percentage of left-handed people in Pelmenia.

E. This is close, but then even right-handers could bail out of the surveys and render this choice unsuitable to help the argument.

Answer choice: D.

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NitishJain · Answer

It is given that there is a difference in %ge of left-handed people of 18 years and elderly people (45yrs, 40 yrs). It is also given that neither percentage of children born left-handed has never changed nor the attitude of people towards them.

The question asks that among the given options which could very help to justify this difference.

Lets pre-think: what if there is some external factor which helps in justifying the observaton.
Assumption 1: what if people leave the town for job and then settle abroad.
Assumption 2: What if there is high mortality rate among the left-handed people after certain age

Let's analyze the options:
A. Wrong as qtn clearly states that percentage of children born left-handed has never changed
B. Wrong, do not help to justify why % of left handers is low for elderly people
C. Out of context
D.  Corrrect  matches with pre-think 2
E. Again out of context.

mSKR · Answer

In the nation of Pelmenia, 20% of 18-year-olds are left-handed, while just 10% of 45-year-olds and 2% of 70-year-olds are left-handed. But the percentage of children born left-handed has never changed in Pelmenia, nor have societal attitudes toward left-handedness.

>> point is why the number of left handed people are falling down?

Which of the following, if true, most helps to explain the variation in left-handedness among Pelmenians?

A) The number of children born each year in Pelmenia has steadily increased over the past seventy years.
>>percentage is mentioned. Total number of children is irrelevant .

B) In Pelmenia, left-handers are no more likely to perish in accidents than right-handers.
>> so they have equal probabilyt of survival , so it couldn’t explain why variation in the number.

C) In Pelmenia, ambidexterity is not considered a desirable attribute.
>>so it could be an assumption to argument but doesn’t explain the variation .

D) In Pelmenia, women have a significantly lower life expectancy than men, and women are also more likely to be born left-handed.-CORRECT 
>> More women are left handed and more women couldn’t survive as they grow . so it explains the variation .

E) As Pelmenians age, they become less likely to participate in surveys regarding handedness or hand dominance
>>it doesn’t tell that only left handed people don’t participate in surveys

MHIKER · Answer

Left-handed people are less than right-handed people as the percentage indicated. The reason why left people as a whole is decreasing will be the answer. Option D gives us the information that women born with left-handed features have less than right-handed people so the percentage of left-handed people is less. The answer is D.

kungfury42 · Answer

GMATNinja  I would really appreciate if you could please help here. I think option E should be correct instead of option D. Here's why:

This option doesn't tell us anything about the sex ratio of Pelmenia. Suppose there are 5 women born for every 1000 men in Pelmenia. And suppose out of every 5 women born, 4 are born left-handed and out of every 1000 men born, 200 are born left-handed.

Now we can see that women are 80% (4/5) likely to be born left-handed and men are 20% (200/1000) likely to be born left-handed which is consistent with the passage that women are more likely to be born left-handed than men.

Now as we can see that since women are significantly fewer in number than men, so even if women have significantly lower life expectancy than men, it wouldn't make any difference in the %age of people who are left-handed as we progress on the age. This eliminates option D.

I want to quote the famous coin-toss example here. Suppose if we toss a coin infinite times, say 100,000,000,000 times we will have a 50%-50% occurence of head and tail in our sample set.

Suppose if we reduce the number of coin tosses to 100,000 we will still have something like 52%-48% occurence of head and tail in our sample set.

But if we reduce the number of tosses to a very small number say 100, we will have nowhere near 50%-50% occurence of head and tail. Maybe we will have 60 Heads and 40 Tails or 75 Heads and 25 Tails.

This is to say that as the sample space reduces, we cannot expect the reduced sample space to follow the same %age pattern as the original sample space. However, as we keep increasing the sample space, the distribution is bound to converge to a value (50-50 in this case)

This serves as a clear evidence that as Pelmenians age and become less participative in surveys regarding handedness we are bound to get skewed results in line with what's shown in the stem.

We cannot assume that a sample space of 100 Pelmenians (at the age of 70) will share the same distribution of handedness as do the 10,000,000 Pelminians (at the age of 18).

Hence, we can say that option E is the correct reason that explains why percentage of left-handed Pelmenians is getting significantly changed as we move up the age groups.

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GMATNinja · Answer

Let's start with (E): In the passage, the data skews in a certain direction -- the percentage of left-handed people goes down dramatically. (E) talks about Pelmenians in general, including both right and left-handed folks. As these Pelmenians get older, they are ALL less likely to participate in surveys. This doesn't explain the specific trend in the data that the passage describes -- why are the left-handed people in particular disappearing? (E) really doesn't give us a reason for this phenomenon. To your point about sample size: sure, the size of your surveyed population does impact how much you should trust that data! However, (E) really doesn't give us enough to say that the sample of 45 year-olds and 70 year-olds is small enough to throw out the results. We have no idea whether the sample size went from a million to nine hundred thousand, or from a million to ten. So, maybe if you squint sideways at it you could say that (E) implies that some of the data isn't perfectly reliable -- but it gives us nothing to explain why the percentage of left-handed people in particular is diminishing. (Also, as a side note: the coin example is a bit off! If you flipped a coin 100,000 times, you'd expect to get heads on about 49.5% to 50.5% of those flips in over 99% of your trials. And if you flip a coin 100 times, a 75/25 split would be an extremely unlikely outlier too -- you might want to get your coin checked for fairness

. So, while sample size definitely matters, it doesn't have as big of an effect as you might think). Compare that to (D): (D) tells us that our left-handers are dying off more quickly than our right-handers, and that gives us a great explanation for why the percentage of left-handedness reduces with age. The edge-case that you've come up with is quite extreme -- you'd really need more information to assume something so outlandish as a skewed brith ratio like the one you're describing. But even in your scenario, if the women are dying earlier than the men, you'd expect the percentage of left-handed people in the population to go down as the population ages. So, (D) would help explain the data. And, even if you've come up with one crazy scenario that makes (D) a bit weaker, that's fine! We're looking for the answer choice that "most helps" to explain the phenomenon, so we don't need a perfect answer choice. (D) gives us a reason that the incidence of left-handedness goes down with age, while (E) does not. So, (D) is our answer. I hope that helps!

Soumanti Roy · Answer

GMATNinja  I am still not clear on why option A is not the right ans. The prompt does tell us that percentage of left-handed children has not changed over the years. I am assuming percentage here means number of left-handed children born divided by number of total children born that year multiplied by 100. In that case, if number of total children born increases then number of left-handed children would also increase even when the percentage does not change. So, younger left-handed people would be more in number.
Besides, both options D and E say that, women are more "likely" to be left-handed and older people are less "likely" to participate in such surveys respectively. In my opinion both of D and E are very similar, both are introducing new information. How are we choosing one over another?
To me, A is better option as we can prove A using data and it mentions the time frame of 70 yrs as well. Please let me know where am I going wrong.

GMATNinja · Answer

You're right that percentage of left-handed children means the number of left-handed children born divided by number of total children born that year multiplied by 100. And if more children are born each year, then yes -- the  number  of left-handers would increase each year.

However, that doesn't explain the data, which says that the  percentage  of left-handers is changing as the population ages. In other words, we don't really care about the  number  of left-handers born each year -- we care about the  proportion  of the population that is left-handed within each age group.

(A) doesn't tell us why this proportion is changing. If the only thing that changes is the number of babies born, then we'd expect the proportion to remain the same. You'd have the same percentage of left-handers among 18-year-olds, 45-year-olds, and 70-year-olds. So, (A) doesn't give us anything to explain why the proportion is, indeed, changing.

So you can eliminate (A).

And sure, the word "likely" shows up in both (D) and (E)! However, there's really nothing similar about the two answer choices -- you have to read each one in turn, and ask yourself whether the information provided would help you to explain the variation in left-handedness among Pelmenians.

For an explanation of these options, check out  this post  and  this one .

I hope that helps!

VerbalBot · Answer

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