Logical ReasoningDifficulty: Hard

PT109 S3 Q8 Explanation

Most people invest in the

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsMust be True

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Stimulus

Most people invest in the stock market without doing any research of their own. Some of these people rely solely on their broker’s advice, whereas some others make decisions based merely on hunches. Other people do some research of their own, but just as often rely only on their broker or on Nonetheless, a majority of investors in the stock market make a profit.

What this question is testing

Must be True

Your task

Break the argument into its conclusion and evidence, then do exactly what the question stem asks with that structure.

Common trap

Answers that sound relevant to the topic but don't connect to the argument's actual reasoning.

Winning move

Predict what a right answer must do, then test each choice against the conclusion-evidence gap.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
8.

If the statements in the passage are true, which one of the following must

Answer choices

  1. Correct69% picked this

    Some people who make a profit on their investments in the stock market do so without doing any

    Why this is right

    This is what we were anticipating. Whenever we know Most A's are B and we know Most A's are C, then at least one member of A has to be both B and C. We know Most [investors] do no research Most [investors] make a profit So we know that at least one person both makes a profit and does no research, which is what this answer choice says.

    Skill tested: Must be True · how this choice captures the argument's function is the move to repeat next time.

  2. Too Strong: most5% picked this

    Most people who invest in the stock market either rely solely on their broker or make decisions

    The first sentence tells us that most investors do no research of their own. Let's pretend that's 51 out of 100 investors. The second sentence says, "Some of the 51 use broker, some of the 51 use hunches". Some = at least one. So out of our 51 investors who do no research, we need a minimum of 1 to rely on broker and 1 to rely on hunches. Thus, out of our 100 investors, only 2 of them can we say for sure "rely solely on broker or decide merely on hunches". But this answer is saying that we know at least 51 of them are that way. The fact that the 2nd sentence only mentions (broker / hunches) as two possibilities for those who don't do their own research doesn't mean that these two possibilities are the only options for investors who do no research. Maybe some look at a crystal ball. Some ask their cat.

  3. Can't Prove Overlap15% picked this

    Some people who do investment research on their own, while just as often relying on their broker or on hunches, make a

    This answer is trying to join traits from Some claims with the "profit" part of the Most claim. We can't prove that Some claims and Most claims overlap. We know that most investors make a profit, so at least 51 of our 100 investors. And the 3rd sentence, which says "Other people do some research on their own, or rely on broker or on hunches" is implicitly a Some statement. If I say, "Some teenagers worry about their social standing. Other teenagers deliver speeches to the UN about climate change", my second statement is just referring to one teenager (Greta Thurnberg). So we only know that there's at least 1 investor who does some research of their own but just as often relies on a broker or hunches. We can't prove that this 1 investor is one of the 51 who make a profit. They could just as easily be one of the 49 who don't make a profit.

  4. Too Strong: most Unknown Most Group9% picked this

    Most people who invest in the stock market without doing any research of their own

    This answer is guaranteed to be wrong, since if it were correct, then answer (A) would also be correct. It's also going to be wrong because it's making a Most claim about a group, and the stimulus never made a Most claim about that group. (A correct answer won't make a Most claim about a group, unless the stimulus also made a most claim about that group). This answer is talking about "most non-researching investors". The stimulus never gave us a fact about "most non-researching investors". The only most claims were the first and last sentences, both of which were about "most investors". (D) is trying to get us to make this illegal move: Most A's are B Most A's are C thus, Most B's are C If I say "most of the people at my wedding were female, and most of the people at my wedding were basketball fans", does that mean that "most of the females at my wedding were basketball fans"? No. There might have been 51 females, 49 males. All 49 males and 11 of the females were basketball fans. Since 60 out of 100 are bball fans, we can say "most people at by wedding were basketball fans". But since only 11 of the 51 females were basketball fans, we can't say that "most of the females were bball fans". That's the same sort of problem with supporting this answer. It might be that the vast majority of investors who make a profit are those who do do their own research. We know that some non-researchers have to make a profit, but it doesn't need to be most of them.

  5. Too Strong: most Unknown Most Group1% picked this

    Most people who rely solely on their broker rather than on hunches make a profit

    This answer is making a Most claim about a group, and the stimulus never made a Most claim about that group. (A correct answer won't make a Most claim about a group, unless the stimulus also made a most claim about that group). This answer is talking about "most people who rely on broker not hunches". The stimulus never gave us a fact about "most people who rely on broker not hunches". The only most claims were the first and last sentences, both of which were about "most investors". We can't possibly quantity what percentage of people who rely solely on their broker end up making a profit; we have no idea whether that percentage exceeds 50% of that group.

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