V21-41

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.

jeffn · Accepted Answer

Official Solution:

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.

General Approach
 
In these kinds of questions, we need to find an answer that justifies the current scenario given the constraints (in this case, that the percentage of left-handed births and societal attitudes towards left-handedness has remained unchanged). In this particular question, the age of the population seems to be the variable affecting the percentage of left-handed individuals. Therefore, we need to find an answer that links this age factor with the declining percentage of left-handed people as the age increases.
 
Correct Answer
 
Explanation D: Suggests that women have a lower life expectancy than men and are more likely to be left-handed. This would mean that as the population ages, there are fewer left-handed individuals since many of the left-handed women have passed away. This would explain why the percentage of left-handed people decreases as age increases, despite the percentage of left-handed births remaining constant.
 
Incorrect Answers
 
A) This answer merely speaks about an increased number of births but does not correlate this with the percentage of left-handed people. Therefore, it does not address why the ratio of left-handed people decreases as age increases.
 
B) This answer eliminates one possible explanation for the decrease in left-handed people (i.e., if left-handers were more prone to accidents). As such, it does not provide a reason for the observed trend.
 
C) This answer addresses the desirability of ambidexterity in Pelmenia but does not provide any connection between ambidexterity and the decrease in left-handers with age. Therefore, it does not explain the trend.
 
E) Even if overall survey participation decreases with age, this does not explain why the ratio of left-handed individuals decreases more so than right-handed individuals as age increases. It merely provides a possible reason for less data, not a justification for the trend. As such, it does not explain the observed percentages.

Answer: D

bb · Answer

Hi. Thank you for the question - it is good you are writing it out. Sometimes CR's need a diagram or a calculation. In this case, however, there is a small caveat. While the number of 70 year olds would be less (e.g. half or a quarter since they were born a long time ago when fewer people were born), the proportion of the left-handed people would not change simply because there are fewer people. The proportion holds the same, no matter the actual number. If you would like to go really deep into it, GMAT Ninja has a lengthy discussion of it here: https://gmatclub.com/forum/in-the-natio ... 51335.html

beebuzz0504 · Answer

How is A wrong?
If population is increasing every year then total born increases . Percentage of left handed remains same but since population is increasing,5% of 100 will be greater than 5% of 200 and hence explains decrease.

Let me know where i went wrong

ayu1989 · Answer

Why is option A wrong.

20% of 100 is less than 20% of 1000. SO if population increases and % remains same, this explains the increasing left hand-ers each year and hence the decrease in their % as the age graph increases.

VerbalTroubleV35 · Answer

Surely the absolute numbers are different when we compare 5% of 100 and 5% of 200 but that is not our area of concern.
The question states that the percentage remains same throughout and hence the absolute numbers are out of scope in the context of the argument.

prakashb2497 · Answer

I got this question right but I have another doubt. This question is tagged under "Resolve a paradox". How is this a paradox? A paradox is a statement or idea that contradicts itself right? What is the contradictory aspect here? Aren't we just finding a explanation to bridge the discrepancy?

KarishmaB   chetan2u   Bunuel

tanishqgirotra · Answer

I believe option (a) and (d) and equally strong point here.

In (a), if we consider 1000 people to be born in x year, out of which 10% are left handed, i.e. 100 people. And then, 2000 people are born in x + 1 year, out of which 10% are left handed, i.e. 200 people and so on... then 100 left handed people born in the x year will age as years pass by, however, the number i.e. 100 will remain the same. On the other hand, number of new born left handed people will keep on increasing as new years come. So, when a survey would be conducted at a particular time, the number of left handed 70 year old's would naturally be less as compared to 20 year olds left handed people. And I personally feel that this explains the variation more validly as compared the option (d).

Please comment.

MyNameisFritz · Answer

Here is my reasoning why we eliminate E:

E: As Pelmenians age, they become  less  likely to participate in surveys regarding handedness or hand dominance.

But how much is  less ? Is it 1% less? 50% less? We can not infer anything from this. Therefore, this is a not a good explanation to the paradox.

gaurikhanna17 · Answer

I did not quite understand the solution. what is wrong with option b ?

8709591791 · Answer

I did not quite understand the solution. But there is no mention of men and women. Can you please explain it in more detail?

miag · Answer

Hi,

Let's break down option D): 
If left-handed people are disproportionately female, and females die younger, then fewer left-handers would survive into older age groups. This would directly help explain why older cohorts have fewer left-handed individuals.

Hope this helps!

shubh8 · Answer

This is a great question that’s helpful for learning and I like the solution - it’s helpful.

V21-41

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards