LSAT 46 - Section 3 - Question 25

This is an MBT question which we know because the question stem reads: If the statements above are true, then which one of the following must also be true?

Our stimulus gives us a set of facts about a plant called “false chicory”--which I can only assume is the sworn enemy of true chicory (kind of like the false chicory Wario to the true chicory’s Mario).

We know that false chicory (why is it false? Does it tell lies?) has a taproot that is half the size of the plant’s height. We also are told that false chicory tends to grow more as it receives more rain. We know that false chicory definitely reaches above average heights if it receives more than twice the average rainfall of its normal habitat.

Notice the shifting from tends to grow taller in sentence two, to always reaches above average heights in sentence three. One happens more often than not, the other always happens.

So what inferences can we make here? Well we know that the taproot is directly proportional to the height of a false chicory (it’s always half the value of the height). We also have some information about what causes the height of a false chicory plant to increase (namely, rain—more specifically twice than average normal rainfall). So can we make some conclusions about what might cause a taproot to grow? I think we can! Anything that makes the false chicory grow taller will also make its taproot grow longer (to exactly one half its height). Therefore rain that contributes to an increase in height would also contribute to a growth in the length of the taproot (that is exactly one half the value of its increase in height).

Cool? Cool!

Now let’s move on to the answer choices:

Answer Choice (A) This is tempting because it's playing on what we know about rain contributing to the height of a false chicory. But all we know about false chicory plants that receive more than twice the standard amount of rain is that they are always above average height. Does this mean that plants that don’t receive this much rain can’t be above average height? No! There may be all sorts of things that contribute to the growth of false chicory and rain is just one of them. There’s also the possibility that both of these plants with different heights received greater than average rainfall. This would mean that they both are above average height, but there would still most likely be a difference in height between them.

Answer Choice (B) So we know that if a false chicory plant has above average height, its taproot will be above average length (because it is always exactly one half of the plant’s height). But this AC has the same error that we found in (A). Receiving more than twice the amount of average rain is sufficient to cause above average height, but that doesn’t mean it’s the only thing that can cause it.

Answer Choice (C) Yet another answer choice that is demonstrating the same error we found in (A) and (B). More than twice the average rainfall is the sufficient condition and above average height is the necessary condition. This answer choice flips the two conditions.

Answer Choice (D) A few problems here. First, to reiterate: there are any number of factors that could contribute to the growth of false chicory. Just because these groups are the same height, does not mean that we can determine if they received the same amount of rainfall. Secondly, this question reads “[if] one group [is] not taller than [another] group,” then those groups must have received the same amount of rainfall. What does this mean? It means the first group could be the same size as the second group, or it could be any other size smaller than the second group. The chicory plants in the second group could all be 6 feet tall compared to the plants in the first group coming in at just over 6 inches tall—this would fit within the parameters set by our stimulus. So even if there was a direct correlation between rainfall and height (and no other factors involved in height), this would not be supported.

Correct Answer Choice (E) We know that if a false chicory plant receives greater than twice average rainfall it will be above average height. We also know that taproots are exactly half the size of the plant’s stalk (or whatever you call the vertical section of a false chicory plant–if you can’t tell by now, I am not a botanist!). Therefore, average taproot length would be exactly one half of average taproot height. So we can definitively say that if receiving more than twice the average amount of rainfall will lead to false chicory plants being above average height, it will also lead to them having taproots that are above average length.