Critical Reasoning

The importance of the ozone layer to terrestrial animals is that it entirely filters out some wavelengths of light but lets others through. Holes in the ozone layer and the dangers associated with these holes are well documented. However, one danger that has not been given sufficient attention is that these holes could lead to severe eye damage for animals of many species.

Which one of the following is most strongly supported by the statements above, if they are true?

A. All wavelengths of sunlight that can cause eye damage are filtered out by the ozone layer where it is intact.
B. Few species of animals live on a part of the earth's surface that is not threatened by holes in the ozone layer.
C. Some species of animals have eyes that will not suffer any damage when exposed to unfiltered sunlight.
D. A single wavelength of sunlight can cause severe damage to the eyes of most species of animals.
E. Some wavelengths of sunlight that cause eye damage are more likely to reach the earth's surface where there are holes in the ozone layer than where there are not.

PowerScore CR Bible Answer E

C is said to be wrong because "many species" may mean "all species". Please explain. If I say I have 10 balls and many balls are red. Can't I be sure that some will not be red?[/spoiler]

Hey hiteshthegame:

But do you really know that you have 10 balls?

What if I were to say that "Many Beat the GMAT members would like to score above 700 on the GMAT." Am I wrong? That's a true statement. But I'd be willing to bet that ALL BTG members would like to score above 700. "All" is just more specific than "many".

In the case of this question it may even be more pronounced. Say that a scientist has studied 100 species of animals and all of them have the potential for eye damage. She can't conclude that "all species" have that potential...there are thousands if not millions of animal species that you'd have to test to prove that "all" of them have this potential. But 100 out of 100...that makes it clear that many species could be affected. Again, "all" is more specific, but if we can't study every single species we may just say "many" since it's not worth the time or effort to prove 'all". But that doesn't mean that "all" is incorrect. The premises are stating what is known, which is that "many species" have this potential. It could be "all species" but given the vast number of species out there we may never know for sure. But until the facts clearly state that there is at least one species that wouldn't be affected - that "not all" species are affected - we cannot prove C to be true.

Brian@VeritasPrep wrote:Hey hiteshthegame:

But do you really know that you have 10 balls?

What if I were to say that "Many Beat the GMAT members would like to score above 700 on the GMAT." Am I wrong? That's a true statement. But I'd be willing to bet that ALL BTG members would like to score above 700. "All" is just more specific than "many".

In the case of this question it may even be more pronounced. Say that a scientist has studied 100 species of animals and all of them have the potential for eye damage. She can't conclude that "all species" have that potential...there are thousands if not millions of animal species that you'd have to test to prove that "all" of them have this potential. But 100 out of 100...that makes it clear that many species could be affected. Again, "all" is more specific, but if we can't study every single species we may just say "many" since it's not worth the time or effort to prove 'all". But that doesn't mean that "all" is incorrect. The premises are stating what is known, which is that "many species" have this potential. It could be "all species" but given the vast number of species out there we may never know for sure. But until the facts clearly state that there is at least one species that wouldn't be affected - that "not all" species are affected - we cannot prove C to be true.

Hi Brian,

Thanks for the explanation. But I am still somewhat not clear on this.

Let's assume I didn't consider any number such as 10, 20 or 100. I am just saying many balls are red. So what you're saying is that all of them being red is also a possibility. Is that correct?

Hi, Kindly find this copy paste stuff..

in this below tree, you can infer DOWNWARDS but NOT upwards:

ALL
MOST
MANY/SOME

Courtesy : Testluv

Hey Hitesh,

Exactly - "many" can still be "all" unless specified otherwise. Again, the logic follows that you may not have been able to observe "all", so your saying "many Xs have Y attribute" doesn't mean "but not all of them do...". It just means exactly what you observed - you've seen many and they have a particular attribute. You can't prove that all of them have that attribute until you've seen all of them, but you can't prove otherwise until you visibly see an exception.

So another example:

I've been to quite a few supermarkets in Los Angeles and one thing I've recently noticed is that they all seem to have hand sanitizers next to the shopping carts so that patrons can wash their hands before and after touching the same cart as dozens of others that day.

So I can logically say: Many supermarkets have hand sanitizers near the shopping carts.

Now, for all I know there may be a state law that mandates this as a public health initiative. It could very well be that all supermarkets in Los Angeles do this now. But I don't know that - I've been to maybe a dozen or so but there are hundreds around here. So all I can prove is that "many" supermarkets have hand sanitizers...but it's definitely conceivable that all of them do. So "many" could be "all"...we'd just have to do a lot more research to find out.


HSPA - thanks for the chart, which should be pretty helpful. I'd just also advise buying into the logic, too - if you click with that (I can only prove what is known and sometimes what is known is less specific than what actually exists) you're taking great strides toward CR mastery.

Hi Brian,
Is supporting a stem different from strengthening it? When I initially read this question, I thought this was a strengthening question. Any comments?


Thanks,
B

Brian@VeritasPrep wrote:Hey Hitesh,

Exactly - "many" can still be "all" unless specified otherwise. Again, the logic follows that you may not have been able to observe "all", so your saying "many Xs have Y attribute" doesn't mean "but not all of them do...". It just means exactly what you observed - you've seen many and they have a particular attribute. You can't prove that all of them have that attribute until you've seen all of them, but you can't prove otherwise until you visibly see an exception.

So another example:

I've been to quite a few supermarkets in Los Angeles and one thing I've recently noticed is that they all seem to have hand sanitizers next to the shopping carts so that patrons can wash their hands before and after touching the same cart as dozens of others that day.

So I can logically say: Many supermarkets have hand sanitizers near the shopping carts.

Now, for all I know there may be a state law that mandates this as a public health initiative. It could very well be that all supermarkets in Los Angeles do this now. But I don't know that - I've been to maybe a dozen or so but there are hundreds around here. So all I can prove is that "many" supermarkets have hand sanitizers...but it's definitely conceivable that all of them do. So "many" could be "all"...we'd just have to do a lot more research to find out.


HSPA - thanks for the chart, which should be pretty helpful. I'd just also advise buying into the logic, too - if you click with that (I can only prove what is known and sometimes what is known is less specific than what actually exists) you're taking great strides toward CR mastery.

Thanks a lot Brian. I got the concept now.

boazkhan wrote:Hi Brian,
Is supporting a stem different from strengthening it? When I initially read this question, I thought this was a strengthening question. Any comments?


Thanks,
B

@Boazkhan, the stem doesn't ask for supporting the stem. The question says which of the answer choices is best supported by statements in the stimulus. This classifies the question as a "must-be-true" question. We are not asked to support or strengthen the stimulus, but to find something that can be concluded from the stimulus.

Great, great point, Hitesh - that word "support" is arguably the trickiest word in CR question stems because it has two uses:

1) The information above best supports which of the following conclusions?
(Your job is to pick the correct conclusion, which must be true based on the premises above)

2) Which of the following best supports the above conclusion?
(Your job is to strengthen the already existing conclusion)

Keep in mind that the premises/facts must support the conclusion. So your job when you see a form of the verb "support" is to determine:

-Are they asking me to use what's given (facts) to support my answer (the conclusion)?

OR

-Are they asking me to use the answer choice (a new fact) to support a given conclusion?

When you see that word "support", slow down and make sure that you think through this decision.

Another hint - if the argument above already has its own conclusion, you're almost always going to be asked to support it. So if you're unsure of the question stem, check the paragraph for:

If it has a conclusion - your job will likely be to strengthen it
If it doesn't have a conclusion - your job is probably to draw one of your own