December 2000 LSAT Section 3 Question 8

Most people invest in the stock market without doing any research of their own. Some of these people rely solely on ...

Anna20 on August 6, 2020

Must Be True

I was stuck between A and C here - and ultimately (and incorrectly) chose C. I thought that C matched the form of the premise (research/don't research --> make a profit). How would you make sure to pick A as the correct answer? To what extent would you consider the quantifiers in this question? Many thanks!

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shunhe on August 7, 2020

Hi @Anna2020,

Thanks for the question! Paying attention to the quantifiers in this question is going to be very important, and in fact the key to getting it right.

So we’re told that most people invest in the stock market without doing any research of their own. Most, remember, means more than half, or “51%.” So let’s say there’s 100 total people investing in the stock market. This means that at least 51 of them invested without doing any research of their own. This sentence is the first key sentence to getting this question right.

Then we’re told that some people rely on broker’s advice, others just go based on hunches, still others research a bit themselves. But still, a majority of investors in the stock market make a profit. This last sentence is going to be the second key sentence. This means most investors in the stock market make a profit. So again, if there’s 100 investors, then at least 51 of them have to make a profit.

So now we know it’s true that there’s a group of at least 51 people who invest without researching. Separately, there’s a group of at least 51 people who make a profit. Let’s assume both these groups are at their minimum; there’s 51 i each. Do they have to overlap? Yes, at least one person has to be in both groups, since there’s 100 total people, and if the two groups were totally separate, they’d add up to 102 people. So at least one person is in both groups. Remember that “some” on the LSAT means “at least one.” So it’s true that some people who make a profit on their investments don’t do research, and that’s how (A) can be definitively proved.

(C), on the other hand, doesn’t have to be true, it’s just a could be true. Because remember, we know that there’s some people who do investment research on their own, while just as often relying on their broker or on hunches. So there’s at least one person like that. But that person could just as easily be in the “not profit” part of the stock market. So (C) doesn’t have to be true.

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