RC - Lyme Disease - GmatPrep

[tim]

Tim, I love your OG archer videos. Its always exciting to hear you explain OG problems. Great job! :o)

Thanks so much! We don't often get much chance for feedback on those videos, and it's good to know they're helping!

[yaoL613]

I picked D because it helps to establish whether there is an alternate way through which ticks can acquire the bacterium and thus we can strengthen or weaken the argument.
...
My reasoning:
Increasing the population of other species that do not harbor the bacterium may help in decreasing the number of ticks that acquire the bacterium - but only when the ticks are in the larvae stage, if deer ticks that were not infected as larvae can become infected as adults, then they do acquire the bacterium and hence the argument is weakened.

nah. you're thinking too hard.

the conclusion of the argument is:
if the population of these other species were increased, the number of ticks acquiring the bacterium would likely decline.

you are mistakenly thinking that ANYTHING that would increase the # of infected ticks is irrelevant to this argument.

you have to stick to this conclusion, though. anything that does not have to do with the CONNECTION between INCREASING THE POPULATION OF OTHER HOST SPECIES and the # of infected ticks ... is irrelevant.

analogy:
let's say the conclusion of an argument is if we institute a gmat prep program at State University, the students' gmat scores will go up.

if i make a statement such as students at State U have recently been getting higher gmat scores because they're studying on their own, this has NO BEARING AT ALL on the conclusion above.
it has to do with increasing gmat scores, but not with the CONNECTION between instituting a prep program and increasing those scores.

OA is B. I am not clear why the size of the deer population is relevant.
The deer population may be limited by the availability of animals on which ticks feed on in larvae stage, but if all these animals are white-footed mice (or any other species that harbor the bacterium) the ticks would acquire the bacterium and in that case the entire deer population is infected. But if all these animals are the 'other species' then ticks would not acquire the bacterium.
So, only the availability of animals does not help in drawing any conclusion, we need to know whether the animals are white-footed mice or the other species.

Can you please explain what is wrong with my reasoning and why B is the correct answer?

heh.

your problem here is that you were looking at the wrong words. someone mistranscribed the problem.
see edits above. (b) should say "deer tick population", not just "deer population".

hope that makes more sense now.

hi ron,

do you mean when the conclusion is" if A(decrease the uninfected hosts), then/so B(the number of ticks acquiring the bacterium would likely decline)", and the question ask us to undermine the conclusion, we should focus on the causal relationship between A and B, and choses include any other factors (deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed) destroy B can not undermine the conclusion.
since even if other factors(deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed) will affect B, the causal relationship between A and B can not be denid.

but if the question is "which of the following if true would not lead to the desired goal/result(the number of ticks acquiring the bacterium would likely decline)"
in this situation, other factor(deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed) undermine B can be correct.
am i correct?
i am very confused about this kind of CR, can you present a more general pattern about it?
thanks a lot!

[RonPurewal]

do you mean when the conclusion is" if A(decrease the uninfected hosts), then/so B(the number of ticks acquiring the bacterium would likely decline)", and the question ask us to undermine the conclusion, we should focus on the causal relationship between A and B, and choses include any other factors (deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed) destroy B can not undermine the conclusion.

the red word should be "increase" rather than "decrease". (also, i'll assume you meant "choices" when you wrote "choses".)

if you're unclear on this stuff, the best way to understand it better is to make an analogy to a situation to which it's easy to apply common sense.

the form of the conclusion here is "if we do x, then y will decrease."

analogy:
If we turn on the air conditioning, the temperature in the room will decrease.
––> obviously, "it's hot outside" does nothing to weaken this statement.

[RonPurewal]

but if the question is "which of the following if true would not lead to the desired goal/result(the number of ticks acquiring the bacterium would likely decline)"
in this situation, other factor(deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed) undermine B can be correct.

no. this is something that's either true or false, so it can't cause a decline in the number of infected ticks.

we can truthfully say something like "the number of infected ticks would be larger if this statement were true than if it were false". this, however, is a fundamentally different type of observation (actual vs. hypothetical) that is irrelevant to the notion of causing a decline.

[RonPurewal]

i am very confused about this kind of CR, can you present a more general pattern about it?
thanks a lot!

the whole point of testing CR is that it's impossible to solve the problems by memorizing "patterns". (if you could actually invent workable "patterns", you would thereby solve some of the most pressing conundrums in artificial intelligence. if that happened, the U.S. government would make you very rich very quickly.)

rather, the point is to consider the specifics of each individual situation.
in other words, you actually have to reason critically. the title is not a lie; you can't bypass it via memorization, no matter how phenomenal your memory might be.

[yaoL613]

do you mean when the conclusion is" if A(decrease the uninfected hosts), then/so B(the number of ticks acquiring the bacterium would likely decline)", and the question ask us to undermine the conclusion, we should focus on the causal relationship between A and B, and choses include any other factors (deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed) destroy B can not undermine the conclusion.

the red word should be "increase" rather than "decrease". (also, i'll assume you meant "choices" when you wrote "choses".)

if you're unclear on this stuff, the best way to understand it better is to make an analogy to a situation to which it's easy to apply common sense.

the form of the conclusion here is "if we do x, then y will decrease."

analogy:
If we turn on the air conditioning, the temperature in the room will decrease.
––> obviously, "it's hot outside" does nothing to weaken this statement.

sorry for my misspelling,
and thx for your reply.

i don't make my question clear, and i will use your analogy to make it clear.

i want to know, if your analogy has the question"which of the following if true would serve to undermine the relationship between temperature and the aircondition."

and if there is a choice"the open window allows the hot air in the outside to flow into the room, conteracting the effect of the aircondition" in your analogy cr,which i think has the same logical mistake as the choice D if D is positive.(Whether deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed)

the choice is incorrect, because although it will have impact on the temperature in the room,but it dosen't mean the air condition can not decrease the temperature.

but if the question is changed into"which of the following, if true, would lead to the undesirable goal(the temperature incrases )" , then the choice"the open window allows the hot air in the outside to flow into the room, conteracting the effect of the aircondition" is correct.

am i make it clear?
am i correct?
thx in advance!

[RonPurewal]

that still wouldn't help, unless the window were opened only when the air conditioner was turned on.
if the window is closed, then turning on the a/c will make the room cooler. if the window is open, then turning on the a/c will still make the room cooler (though not as cool as it would be if the window were closed).

in any case, i think you get the point in terms of the original problem + choices. at this point we've strayed into discussing imaginary variations of imaginary problems, so that should probably end here.

[yaoL613]

thanks a lot
it really helps!

[RonPurewal]

sure.

[BarbieC342]

Dear Ron,
After spending nearing 2.5 hours in reading the whole thread, I think I finally get your logic and explanation.
Thank you so much for patient explanation!
Wish you happy everyday.

[RonPurewal]

no problem; glad it helped.

by the way, if there's any one particular CR problem that just confounds you completely, the best thing to do is just to let it go.
if that's the case, then the issue probably just has something to do with the specific wording of the problem and/or answer choices--i.e., something that won't generalize at all, in any way, to other problems.

[BarbieC342]

Dear Ron,
You are right that I'm confused because I am not familiar with some wording and expressions, but I'm trying hard to know these subtle meanings so I spend time reading each of your replies. It's like talking to a mystic friend and it really helped. Thank you~

[RonPurewal]

you're welcome.

this particular problem has frustrated a huge number of students, so you're not alone there.

[imperial.franco]

I'll try a different approach. It may be easier for some?

How to accept choice B as the correct answer: "Whether the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on."

Let S = {t, t, t, t, o, o, m, m, m}
in which S = status quo ecosystem, t = ticks, m = mice, o = other species.

In the current ecosystem, assume 4 ticks consume 2 o's and 2 m's. Hence, we have 1 m left uneaten, and 2 t's are infected.

Evaluate answer choice B:
"Yes, the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on."

S = {t, t, t, t, m, m, m, o, o} --> S' = {t, t, t, t, t, t, t, t, o, o, o, o, m, m, m}
- in this scenario, assume that doubling the o's causes t's to double. Hence, 7 t's eat 4 o's, and all 3 m's. (We can even argue that the extra t may even gobble up the corpse of 1 m). So we have all 3 m's eaten, and 4 t's infected. (Weakens as the plan resulted in an increase in t's.)

"No, the size of the deer tick population is not limited by the availability of animals for the tick's larval stage to feed on."
S = {t, t, t, t, m, m, m, o, o} --> S' = {t, t, t, t, o, o, o, o, m, m, m}
- in this scenario, doubling the o's does not change the number of t's. Hence, 4t's eat all o's. So we have all 3 m's uneaten, and 0 t's infected.
(Strengthen as the plan worked. i.e. number of ticks eating mice declined)

Yes, this analysis is simplistic. However if you extend this to a larger scale (real ecosystem), this simplistic scenario may work. (If we extend to a larger scale, we will deal with probabilities. i.e. probability increases that t's will eat m's as we increase number of t in the ecosystem; On the other hand, the probability decreases that t's will eat m's if t's are unchanged but there are more o's to available for t to eat.)

[RonPurewal]

sure, the key ideas are in there -- but the point is that you should be able to understand, very generally, how changes in certain quantities will affect other quantities WITHOUT having to do actual mathematics.

if a problem required this sort of approach, it would appear in the quant section rather than in CR.