Left-handed persons suffer more frequently than do right-handed person

Question

Left-handed persons suffer more frequently than do right-handed persons from certain immune disorders, such as allergies. Left-handers tend to have an advantage over the right-handed majority, however, on tasks controlled by the right hemisphere of the brain, and mathematical reasoning is strongly under the influence of the right hemisphere in most people.

If the information above is true, it best supports which of the following hypotheses?

(A) Most people who suffer from allergies or other such immune disorders are left-handed rather than right-handed.

(B) Most left-handed mathematicians suffer from some kind of allergy.

(C) There are proportionally more left-handers among people whose ability to reason mathematically is above average than there are among people with poor mathematical reasoning ability.

(D) If a left-handed person suffers from an allergy, that person will probably be good at mathematics.

(E) There are proportionally more people who suffer from immune disorders such as allergies than there are people who are left-handed or people whose mathematical reasoning ability is unusually good.

ChrisLele · Accepted Answer

The key to this question is to not forget that the proportion between left-handers and right-handers is skewed. Therefore, just because lefties are more likely to have allergies then righties does not mean that if somebody has allergies he/she is more likely to be lefty. After all, if 90% of population is righty, then there are far more righties and we can't draw this conclusion. (C) takes this phenomenon into account. If lefties are stronger at math, then proportionally you will see more lefties in an above average math group than a below average group.

GMATNinja · Answer

This question is asking which hypotheses is best supported by the information in the passage. Let's take the answer choices on by one:

We know that "left-handed persons suffer more frequently than do right-handed persons from certain immune disorders." So if you picked a random group of say 100 left-handed people and another random group of 100 right-handed people, you'd expect more of the left-handed people to have immune disorders. But this doesn't mean that  most people  who suffer from immune disorders are left-handed, as answer choice (A) says.

That's because we don't know the balance of left-handed versus right handed people  in general . If the majority of people are right handed, for example, there could still be more right-handed people with immune disorders, even if right-handed people suffer from immune disorders less frequently. Since the hypothesis that  most people  who suffer from immune disorders are left-handed is not supported by the passage, (A) is out.

Just because left-handed people suffer from immune disorders such as allergies more frequently than do right-handed people, this doesn't mean that  most  left-handed people have some kind of allergy. If only 1% of right-handed people have an allergy, for example, then the percentage of left-handed people with allergies could be as low as 2% (or 1.000001%) - so definitely not  most  left-handed people. (B) is out.

The passage tells us that left-handers tend to have an advantage over the right-handers on "tasks controlled by the right hemisphere of the brain." Additionally, we learn that "mathematical reasoning is strongly under the influence of the right hemisphere in most people."

So if  mathematical reasoning  is largely controlled by the  right hemisphere , and if left-handers have an advantage over right-handers on tasks controlled by the right hemisphere in most people, we'd expect that left-handers would  generally  have an advantage over right-handers when it comes to  mathematical reasoning .

Following this logic, if we took a random sample of left-handers and a random sample of right-handers, we'd expect the mathematical ability of the left-handers to be higher in general. And if that were true, more of the left-handers would have above average mathematical abilities than the right-handers. Let's hold on to (C).

The passage makes no connection between left-handed people who suffer from  allergies  and left-handed people who are  good at mathematics . And although we'd expect left-handers to have an advantage over right-handers in terms of mathematical ability, that doesn't tell us whether  any particular  left-hander is " good at math ." Since it's not supported, (D) is out.

The passage doesn't tell us anything about the proportion of people  in general  who suffer from immune disorders. Nor does it tell us much about what proportion of left-handed people are good at mathematical reasoning -- aside from the fact that the proportion is bigger than it is for right-handers. As a result, we have  no basis  to compare these two groups of people, and (E) is out.

So we're left with (B).

I hope that helps!

seekmba · Answer

Left-handed persons suffer more frequently than do right-handed persons from certain immune disorders, such as allergies. Left-handers tend to have an advantage over the right-handed majority, however, on tasks controlled by the right hemisphere of the brain, and mathematical reasoning is strongly under the influence of the right hemisphere in most people.

If the information above is true, it best supports which of the following hypotheses?

(A) Most people who suffer from allergies or other such immune disorders are left-handed rather than right-handed. - the argument more LH suffer from allery not that most people who suffer from allergies are LH. Argument If A then B and this option says If B then A. incorrect

(B) Most left-handed mathematicians suffer from some kind of allergy. - most LH suffer from allergies not most LH mathematicians suffer from allergies

(C) There are proportionally more left-handers among people whose ability to reason mathematically is above average than there are among people with poor mathematical reasoning ability. (correct) - argument says LH have advantage on tasks controlled by the right hemisphere of the brain, and mathematical reasoning is strongly under the influence of the right hemisphere.

(D) If a left-handed person suffers from an allergy, that person will probably be good at mathematics. - Argument says LH suffers frequently from allergies and LH have advantage on tasks controlled by right hemisphere...and so good in mathematics....that does not mean that if a LH has allergy, he is also good at mathematics.

(E) There are proportionally more people who suffer from immune disorders such as allergies than there are people who are left-handed or people whose mathematical reasoning ability is unusually good. - irrelevant

nepr9 · Answer

Why is Option D wrong? We know that left-handed person will probably be good at maths since most lefties are..

svasan05 · Answer

Hi

The problem with option (D) is the causal relationship (in the minimum, a correlation) it draws between having allergies and being good at Mathematics. From the stimulus, we know the following:

i) Left handers are more susceptible to immune disorders like allergies.
ii) Left handers are likely to be good at skills like mathematics.

Option (D) states:   If a left-handed person suffers from an allergy , that person will probably  be good at mathematics .

This restricts the universe to those left handers who suffer from allergies. However, the fact of left handers being good at mathematics is true not only of such left handers who suffer from allergies, but all such left handers in whom the skill is controlled by the right hemisphere of the brain. Hence this is not a valid conclusion that can be drawn from the facts presented in the stimulus.

Hope this clarifies.

sudeshpatodiya · Answer

@savasan05

"This restricts the universe to those left handers who suffer from allergies. However, the fact of left handers being good at mathematics is true not only of such left handers who suffer from allergies, but all such left handers in whom the skill is controlled by the right hemisphere of the brain. Hence this is not a valid conclusion that can be drawn from the facts presented in the stimulus."

The option is not restricting to left handers who have allergies. It's just stating a condition here. If they have allergies, they probably are good at mathematics.

Are you suggesting that the option also implies that "If left handers do not have allergies, they are probably not good at mathematics" ?
If not, then how is it restricting?

Please can you elaborate.

svasan05 · Answer

Hi Sudesh

The problem here is the causal relationship drawn between having allergies and being good at mathematics, while the correlation is actually between being a left hander and being good at math.

That is one of the possible interpretations of the statement given in option (D). It is not certain that if they do not have allergies, they are not good at math, but a possibility based on the way the option is worded. A left hander without allergies may or may not be good at math. Hence, what can be said with certainty about being good at math is restricted to left handers who have allergies.

Hope this clarifies.

Sidharth003 · Answer

GMATNinja   GMATninja2   AjiteshArun  I marked C because that is a strong hypothesis, but while doing the POE got stuck with E. Kindly help me fill the gap in my logic. Here is my understanding of option E:

"There are proportionally more people who suffer from immune disorders such as allergies than there are people who are left-handed or people whose mathematical reasoning ability is unusually good."

People who have immune disorders can be RH or LH( the frequency being greater for LH people), so number of people having immune disorders is definitely more than LH as the RH also have Immune disorders. LH have better reasoning ability so this is again a subset of LH people which is less than immune disorder sufferers.

So why can't we say without a doubt that E is a valid hypotheses?

AjiteshArun · Answer

Hi  Sidharth003 ,

Let's focus on the first half of E: "There are proportionally more people who suffer from immune disorders than there are people who are left-handed".

(a) The proportion of people who suffer from immune disorders is (the number of left-handed people with immune disorders  plus  the number of right-handed people with immune disorders)  divided by  (the total number of people, which is nothing but the number of left-handed people  plus  the number of right-handed people).

(b) The proportion of left-handed people is simply the number of left-handed people (LH)  divided by  the total number of people (LH + RH).

Now, option E says that (a) > (b). In other words, it says that (LH_ID + RH_ID)/(LH + RH) is greater than LH/(LH + RH). The denominators are the same, so we should focus on the numerators. Is (LH_ID + RH_ID) > LH  or  is LH > (LH_ID + RH_ID)?

We know that LH_ID < LH (as long as the percentage of lefties with immune disorders isn't 100%), but we have no idea what RH_ID is. Maybe RH_ID isn't large enough to make (LH_ID + RH_ID) > (LH). Or maybe it is. We can't say.

anshul0130 · Answer

GMATNinja  - Can you pls explain this argument in detail as I didn't get this thoroughly ?

Thanks,
Anshul P

Nina1987 · Answer

is that mistaken reversal? is it helpful to know these logic rules, cuz then we can eliminate such answer choices quickly w/o having to think thru them? thanks

GMATNinja · Answer

These are critical "reasoning" questions, and there's really no way to accurately answer them without actually reasoning your way through each one. When you attempt to memorize certain patterns, we've found that it's just too easy to misread a passage or answer choice to make it fit those patterns.

So, while we understand the appeal of memorizing rules, we don't recommend it for GMAT CR. For more on the approach that we do like, check out  this article  or  this video .

I hope that helps a bit!

Raman109 · Answer

Left-handed persons suffer more frequently than do right-handed persons from certain immune disorders, such as allergies. Left-handers tend to have an advantage over the right-handed majority, however, on tasks controlled by the right hemisphere of the brain, and mathematical reasoning is strongly under the influence of the right hemisphere in most people.

What is given is 
1. LH suffers more frequently (the frequency) from immune disorders than RH
2. LH has an advantage over RH on tasks controlled by the right hemisphere (maths reasoning)

Option Elimination -

(A) Most people who suffer from allergies or other such immune disorders are left-handed rather than right-handed. Suppose the population is 100 - 90% RH and 10% LH. And if 10% of RH suffer from allergies (9 people) and 20% of LH suffer from allergies (it has to be more than RH) - 2 people. Wrong. Moreover, the number of people is not even mentioned in the argument. At best its out of scope.

(B) Most left-handed mathematicians suffer from some kind of allergy. - Might be true. We don't know. What if we take the same example as in A. out of 10, most are 8 who don't suffer from allergies? Wrong.

(C) There are proportionally more left-handers among people whose ability to reason mathematically is above average than there are among people with poor mathematical reasoning ability. - makes sense.

(D) If a left-handed person suffers from an allergy, that person will probably be good at mathematics. No such correlation has been established. Out of scope.

(E) There are proportionally more people who suffer from immune disorders such as allergies than there are people who are left-handed or people whose mathematical reasoning ability is unusually good. Number of people is not even discussed. Out of scope.

KarishmaB · Answer

Premises: Left-handed persons suffer more frequently than do right-handed persons from certain immune disorders, such as allergies. (Of 100 LHPs, say 20% have allergies while of 100 RHPs, only 5% have allergies) Left-handers tend to have an advantage over the right-handed majority, however, on tasks controlled by the right hemisphere of the brain, and mathematical reasoning is strongly under the influence of the right hemisphere in most people. (LHPs tend to have better mathematical reasoning than RHPs) We need an option that is supported by these premises. (A) Most people who suffer from allergies or other such immune disorders are left-handed rather than right-handed. Not correct. Trap answer. We know that RHPs are majority. So in a population of 1000, say 100 are LHPs and 900 are RHPs. 20% of LHPs means 20 people have allergies while 5% of RHPs means 45 people have allergies. So overall, in the allergies group, we could have more RHPs. I suggest using sets to understand this. Screenshot 2024-12-05 at 1.56.58 PM.png (B) Most left-handed mathematicians suffer from some kind of allergy. We don't know what the proportion of allergies are in the LHPs. Also, 'better at Math reasoning' and Mathematician are widely different sets. (C) There are proportionally more left-handers among people whose ability to reason mathematically is above average than there are among people with poor mathematical reasoning ability. The key word here is "proportionally". If 10% of the population is LHPs, we would expect 10% of LHPs in the "people whose ability to reason mathematically is above average" group. But since LHPs are better at reasoning mathematically, we can expect a higher percentage of LHPs in that group. Also, we can expect that in the "people with poor mathematical reasoning ability" group, there will be fewer than 10% LHPs. So we can infer this statement. (D) If a left-handed person suffers from an allergy, that person will probably be good at mathematics. Allergy and math ability are not correlated in LHPs. It is not given that those with allergies are better at Math. Just that overall LHPs are better at Math and overall more of them have allergies. There is no conditional relation between allergies and Math. (E) There are proportionally more people who suffer from immune disorders such as allergies than there are people who are left-handed or people whose mathematical reasoning ability is unusually good. We don't know the relative numbers of those who have allergies, those who are LHPs and those who are good at Math. Answer (C)

Left-handed persons suffer more frequently than do right-handed person

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Left-handed persons suffer more frequently than do right-handed person

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