In an experiment, subjects were shown a series of images on a computer screen, appearing usually at the top but occas...

mamie on November 3, 2019

I think because it is a "must be true" question, answer E mentions that it is "rational" but the stimulus never mentions anything about rationality. For must be true questions you can only chose the answer that does not interject any outside the stimulus information. When I answer must be true questions you look to see if the answer choice just mentions information in the stimulus.

hfatima1 on April 26, 2020

I do not understand how I would shorthand this question to get to the answer or what strategy I would use. I find questions like these difficult with the parallel reasoning. Can you explain the setup and strategies please, and recommend any office hours that discuss this?

jingjingxiao11111@gmail.com on June 5, 2020

Hi I am not an instructor but I was able to get to the correct answer from the sentence, “Instead, if they had simply guessed that the next image would always appear at the top, they would have been correct most of the time.”

The word “instead” at the beginning of the sentence tells us this is not the case that happened in the experiment. Thus, it must mean that some participants had chosen some downs, and some of these downs must have been incorrect. If all participants had chosen all down guesses correctly, they would have guessed correctly 100% but this violates the stimulus condition “instead, had they chosen up all up all the time, they would have been correct most of the time.” Also guessing all down correctly by all participants would make the participants correct 100%, thus violating another condition in the stimulus “They guessed correctly less than half of the time.”

And the quantifier “some” is nice since we don’t know the percentages of their guess down that were incorrect so any stronger quantifiers such as “most” or “all” would have made this answer choice not directly supported by the stimulus passage.

I hope that I explained it correctly. Please feel free to correct me. Thank you

hfatima1 on August 4, 2020

thank you, I found that very helpful!!

shunhe on August 4, 2020

Hi everyone,

Thanks for the question! I’ll try to give another perspective on why (E) is incorrect and why (D) is correct. Let’s take a look at the stimulus first. So first, we’re told that in this experiment, people look at a bunch of images on a computer screen. Usually, they’re at the top, and sometimes, they’re on the bottom. And they’re supposed to guess what the next image is going to be. Now, they actually guessed wrong more often than they guessed right, basing their guesses on patterns they thought they saw. But if they just always guessed top they would’ve been right most of the time.

So now we’re asked for something that must be true. This is going to be something that we can infer directly from a statement, or restates a statement, or combines statements. First, (E) tells us that what must be true is the fact that the most rational strategy for guessing correctly would’ve been simply to always guess the image would appear at the top. One reason this is wrong, as some people have mentioned, is because “rationality” isn’t mentioned anywhere, so we can’t make any claims about it based on the stimulus. Another reason is that even if we assumed that the most rational thing to do were to get as many right as possible, we aren’t told that just guessing the top would be the BEST strategy. Maybe the best strategy in that regards would be to guess top 90% of the time, and randomly throw in some bottom guesses. So nothing suggests rationality or “the most” rational, and (E) is wrong.

(D), on the other hand, tells us that some of the subjects sometimes guessed that the next image would appear at the bottom of the computer screen, but were incorrect. And this has to be true! If it were false, then none of the subjects sometimes guessed that the next image would appear at the bottom of the computer screen, but were incorrect. In other words, whenever the subjects guessed bottom, they were correct! And that means that overall, they would’ve gotten more than half the questions right, since the other times they would’ve guessed top, and the correct answer was usually top. But that’s not what happens, so (D) has to be true.

Hope this helps! Feel free to ask any other questions that you might have.

jingjingxiao11111@gmail.com on September 7, 2020

Wow Thank you very much Shunhe! Your answers always help me in my studies!