PrepTest 109

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Invest—most—not Do own research
Invest—most—Make profit

Answer Anticipation:
We're going to start with the inference that can be derived from the two statements in our Summary, which leads straight to the correct answer, and then take a step back to walk through why we focused on only those two statements.

First, two most statements that share a first term can be combined to form a some statement linking the unshared terms:
not Do own research—some—Make profit
This is the only valid inference to be drawn from the stimulus, and it ends up being the right answer.

Now, how did we know to focus on only those two statements? When working with quantifiers, some statements can be combined only with conditionals, not most statements. Since this stimulus started with a most statement and had a some statement second, we scanned through to see if there were any conditionals. There weren't—just some and most statements—so we knew that the inference was going to come from the most statements.

One note on that—the second—to—last sentence. It opens in a conditional manner ("Only") but then it uses language that changes the conditional into a quantified statement—"Only a few" means so do but most don't. Diagramming that statement out you'd end up with a statement that matches the first so we didn't bother!

Answer Explanation:
Make profit—some—not Do own research. This matches our anticipation. Remember—some statements are reversible. This answer is derived by combining the first and last statements—the only ones that could be validly combined.

Key Takeaway:
Know your quantifier rules! Not only will they help you draw inferences from quantifier statements but they'll let you know what statements can even be combined in the first place streamlining your process. Here we were able to skip over diagramming most of the statements since we knew they wouldn't lead to inferences.

Incorrect. "Some" of "most" people fall into these two categories but some of most isn't most.

Incorrect. This group of people was introduced as "[o]ther people" which we can read only as a some statement and thus can't draw this inference from.

Incorrect. This answer is too strong, as combining two most statements yields a some statement.

Incorrect. The statements about taking a broker's advice aren't strong enough to yield an inference—they're about "[s]ome" of the people who don't do their own research or "[o]ther people."