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#21 - The energy an animal must expend to move uphill is

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Complete Question Explanation

Assumption. The correct answer choice is (C)

This stimulus gives you two main premises to arrive at its ultimate conclusion. First, the energy an animal must expend to go uphill is proportional to its body weight; and second, the animal's energy output available to go up hill is proportional to its surface area. These premises are used to jump to a conclusion that this is why small animals maintain their speed while going uphill while large animals slow down. We are missing a key piece of information however in making that jump. Since this is an assumption question, we must identify that missing piece of information.

Answer Choice (A): The information provided in the stimulus already supports the truth of this statement. Since we are told that the energy necessary to go uphill is proportional to body weight, it would have to follow that large animals would be required to expend more energy.

Answer Choice (B): The overall speed of large and small animals is not the issue here. The issue the stimulus is addressing is how much each size of animal slows down from their normal speed when forced to go uphill.

Answer Choice (C): This is the correct answer choice. If the ratio of surface area to body weight is smaller in large animals than it is in small animals, it would follow that the small animals would have more energy available to them to go uphill in relation to the amount of energy they must expend in doing so.

Answer Choice (D): This answer choice is basically the negated version of Answer Choice (C). As such, it weakens the stimulus argument and should be quickly dismissed.

Answer Choice (E): Just as in Answer Choice (B), this answer fails to address the correct issue. The energy needed to run at a given speed is irrelevant to the stimulus argument. The issue the stimulus is addressing is how much each size of animal slows down from their normal speed when forced to go uphill.
tizwvu34
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I'm having a hard time understanding what constitutes a larger ratio compared to a smaller ratio. Does a larger ratio simply have a bigger difference between the two numbers? (i.e. 1:100 is a larger ratio than 1:10)

What about a 1:10 ratio compared to a 10:1 ratio?

I guess my confusion comes in comparing two ratios and how the term larger and smaller is applied. Thank you for the clarification and any light you can shed on the topic of ratio's in the LSAT.
Jonathan Evans
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Hi, Tizwvu,

Good question. These kinds of problems that require knowledge of math concepts such as ratios are somewhat uncommon, with the exception of problems that test relationships between actual numbers and percentages. With that caveat, it is clear that you cannot rule out questions that test some understanding of proportions and ratios. Fortunately, the meaning of larger ratio versus small ratio here is actually quite straightforward.

Consider the premises:

1) Energy required to move uphill is proportional to body weight. ER : BW

2) Energy available is proportional to surface area. EA : SA

Conclusion:

Small animals can move faster uphill than can large animals.

Necessary assumptions:

1) Rate at which animals can move is proportional to the extent to which their energy available exceeds the energy required to perform a task.

2) Surface area of small animals must be larger relative to their body weights than the surface area of large animals relative to their body weights.

In other words, given that a 100 lb animal requires more energy to move up a hill, a lower surface area would constrain the amount of energy available.

Given that a 5 lb animal requires less energy to move up a hill, a greater surface area would give it more energy available, more easily exceeding the energy required.

Should we have trouble with prephrasing for this problem, we can consider Answer Choice (C) and perform the Assumption Negation Test on it.

Answer Choice (C) states: "The ratio of surface area to body weight is smaller in large animals than it is in small animals."

Which brings us to your question " (i.e. 1:100 is a larger ratio than 1:10) What about a 1:10 ratio compared to a 10:1 ratio?"

The answer is a 10:1 ratio > 1:10 ratio > 1:100 ratio. Expressed as fractions these are 10 > 1/10 > 1/100

This answer (C) matches our prediction as stated above, but now let's negate it:

"The ratio of surface area to body weight is NOT smaller in large animals than it is in small animals."

In other words, SAB : BWB is greater than or equal to SAS : BWS

If the surface area of larger animals were commensurately greater to match their larger body weight compared to this ratio in smaller animals, our conclusion that this relationship explains smaller animals' ability to move uphill faster makes no sense.

I hope this explanation helps.
mariahenain
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I'm really having trouble understanding this argument as whole, not because of the structure but because of the content. I eliminated A and B, but then got confused between the rest of the answer choices. What are the general takeaways/patterns for this question? How can I move to the next assumption question without getting bogged down by the details/content?
Adam Tyson
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Never let content be a barrier that slows you down, mariahenain. This one is dense for sure, and if you get truly lost in the details you should hit the eject button by guessing and moving on. That said, I find that it's useful to break down stimuli like this one by paraphrasing, making each statement into something easier to deal with. Here's how I would do that with this stimulus:

First sentence: The more you weigh, the more energy you need to climb a hill

Second sentence: The bigger your surface area, the more energy you have available

Third sentence, the conclusion: little animals maintain their speed while big ones slow down

The assumption stem means there is a gap in the argument, and we need to connect the premises in the first two sentences to the conclusion in the last sentence. Look for answers that connect the ideas to each other, something like "little animals have more energy than big ones" or "little animals have a lot of energy compared to big ones". These aren't perfect prephrases - they don't exactly capture the ratio idea of surface area to weight - but they might get you close. It isn't that small animals are faster than big ones, so answer B gets tossed out. It's definitely about animals of different sizes differing from each other in other ways, so answer D is a loser.

Look for ways to connect the ideas in the premises - weight and surface area - to the new ideas in the conclusion - small animals and big animals. That might be enough to narrow it down to the correct answer here, which is C, because answers A and E, the only remaining choices, say nothing about weight. A also fails to mention surface area, and E says nothing about different sizes. That mechanical approach can be very helpful when the details and content of the stimulus are overwhelming or confusing.

Ultimately, don't let content get in your way. If you must, just guess and move on, and come back to it later if time allows. Be willing to give up that battle on the way to winning the war.

Good luck!
Adam M. Tyson
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Blueballoon5%
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Adam Tyson wrote:Never let content be a barrier that slows you down, mariahenain. This one is dense for sure, and if you get truly lost in the details you should hit the eject button by guessing and moving on. That said, I find that it's useful to break down stimuli like this one by paraphrasing, making each statement into something easier to deal with. Here's how I would do that with this stimulus:

First sentence: The more you weigh, the more energy you need to climb a hill

Second sentence: The bigger your surface area, the more energy you have available

Third sentence, the conclusion: little animals maintain their speed while big ones slow down

The assumption stem means there is a gap in the argument, and we need to connect the premises in the first two sentences to the conclusion in the last sentence. Look for answers that connect the ideas to each other, something like "little animals have more energy than big ones" or "little animals have a lot of energy compared to big ones". These aren't perfect prephrases - they don't exactly capture the ratio idea of surface area to weight - but they might get you close. It isn't that small animals are faster than big ones, so answer B gets tossed out. It's definitely about animals of different sizes differing from each other in other ways, so answer D is a loser.

Look for ways to connect the ideas in the premises - weight and surface area - to the new ideas in the conclusion - small animals and big animals. That might be enough to narrow it down to the correct answer here, which is C, because answers A and E, the only remaining choices, say nothing about weight. A also fails to mention surface area, and E says nothing about different sizes. That mechanical approach can be very helpful when the details and content of the stimulus are overwhelming or confusing.

Ultimately, don't let content get in your way. If you must, just guess and move on, and come back to it later if time allows. Be willing to give up that battle on the way to winning the war.

Good luck!


Hello! In the context of this question, what does "surface area" mean? Does this mean the distance of the uphill? Or something else?

Additionally, if it is distance, how is this possible: "The bigger your surface area, the more energy you have available"? For example, if I have to run a longer distance uphill, wouldn't I have less energy available?

(I haven't taken a math course since high school, so my math knowledge is a little rusty).
Brook Miscoski
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Blueballoon,

The stimulus contrasts the animal's "weight" to the animal's "surface area," but doesn't provide further information about "surface area." Thus, "surface area" has its standard meaning. For an animal, you would loosely think of its surface area as its skin or hide.

However, you don't need to understand geometric formulas in order to get this correct. All you need to understand is that the stimulus claims that the ratio of weight (energy required) to surface area (energy available) is why smaller animals are better at moving uphill. Thus, the stimulus claims that small animals have more available energy, which only makes sense if they have a more advantageous ratio of surface area to weight--answer choice C.