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

[James Finch]

Hi Jay,

As the OP explanation states, (D) has the opposite effect on the argument that (C) has, in that it implies that small animals would have a very similar weight-to-surface area ratio compared to large animals. If this is true, then the stimulus's causal argument goes out the window, because we would have the same effect (very different climbing abilities between large and small animals) without the stimulus's assumed cause (very different weight-to-surface area ratios between large and small animals).

When negated, this should be clear:

Lots of variation in the ratio Ratio differences explain climbing differences

Clearly this doesn't make sense, more variation would be evidence for the conclusion as given, not its negation. Remember when using the Assumption Negation technique you must negate both the answer choice and the conclusion. Contrast this to the negation of (C):

No variation in ratio between large and small animals Ratio differences explain climbing differences

Makes perfect sense, since you can't use something that doesn't exist to explain anything.

Hope this clears things up!

[bluebell]

For the life of me, I cannot understand neither the stimulus or the correct answer choice. Can someone please dumb this down for me?

[Adam Tyson]

Happy to try, bluebell!

The stimulus tells us that there are two proportions at work, and that should clue us in that this question is probably going to be about numbers and percentages. In other words, math - ugh.

The first proportion means that the more you weigh, the more energy you need to move uphill. The second ones tells us that the bigger you are, the more energy you have to move uphill. The author then concludes that these two proportions indicate why squirrels (that weigh little and have little surface area) can move upwards faster than big animals (heavier, more surface area) can. But why? Don't the big animals have more surface area, and thus more total energy available, than squirrels? Shouldn't bigger animals move just as fast as smaller ones?

The author must be assuming something to do with the ratio of energy available to the weight of the animal, which determines the amount of energy needed. Squirrels must have more energy, relative to their weight, than bigger animals have. If that wasn't true, then this argument would make no sense, and we would need another explanation for a squirrel's amazing ability to race up a tree. Look for an answer that is about that ratio! In particular, we need an answer that tells us that there is a difference between smaller animals and larger ones that would explain the difference in their abilities. Answer D talks about the ratio, but not about the difference, so it's a problem. Answer C, the correct answer, talks about the ratio AND about the difference, and that's why it's a winner, even if you don't totally follow the math of it!

[KwakuS]

Hello,

Thank you for your response Adam. I, like bluebell, had no idea where to even start with this question. Now I think I understand it better, so I'm going to walk through it and see if I get what it means.

So now I get that the stimulus was just a really convoluted way of saying that if the animal is heavier, it needs to expend more energy to move. If it has a bigger surface area, it has more energy to expend. So from that standpoint, big animals and small animals should move just as quickly, meaning there is some hidden assumption that we are not seeing. Then you go to the answer choices:

A. I don't think this is true. Larger animals need to expend more energy, based on the stimulus, so I think that rules out this one
B. This is just a restatement of a fact in the stimulus
C. The word "ratio" is what threw me off. Ratio does not always mean that the absolute number of something is less than another (i.e. a ratio of 1/4 of 20 pizzas still gives me more pizzas than a ratio of 1/2 of 4 pizzas) But I think that's what this is trying to say - that smaller and larger animals, in this question at least, have relatively equal surface areas, but larger animals have more weight, making smaller animals faster. That makes sense to me. But ratio I felt was a bit ambiguous. What did I miss here? How could I have read this better?
D. This brings up ratio again. But if there is little variation between, I guess that leaves us back at square one where they have the same speed and doesn't explain the difference. Is that a good way of looking at it?
E. This seems pretty similar to a restatement of the fact about surface area and energy output, just with "at a given speed" added to it.

Hopefully, I didn't make things more confusing.

Thanks,
Kwaku

[Adam Tyson]

I think this looks good, Kwaku! The only thing you are missing is in seeing that the stimulus talks about proportions, which are equations in which ratios are equal to each other. That's why a smaller ratio matters - it changes the proportions.