Critical Reasoning

nandy1984 wrote:In an experiment, two-year-old boys and their fathers made pie dough together using rolling pins and other utensils. Each father-son pair used a rolling pin that was distinctively different from those used by the other father-son pairs, and each father repeated the phrase "rolling pin" each time his son used it. But when the children were asked to identify all of the rolling pins among a group of kitchen utensils that included several rolling pins, each child picked only the one that he had used. Which one of the following inferences is most supported by the information above?
a) The children did not grasp the function of a rolling pin.
b) No two children understood the name "rolling pin" to apply to the same object.
c) The children understood that all rolling pins have the same general shape.
d) Each child was able to identify correctly only the utensils that he had used.
e) The children were not able to distinguish the rolling pins they used from other rolling pins.

Since the inference questions must be proved from the above statements without any additional assumptions (a) talking about the function is wrong... (d) seems to be generalizing on all the utensiles rather than talking about the rolling pins, which the passage is interested in...Can any one help me how the other choices can be eliminated?... And it would be of great help if you can briefly explain the Inference questions...Thanks

Hi nandy1984!

The key to inference is to avoid making ANY assumptions (something we often do when talking about "inferences" in the real world. For example, if I walked into the room with wet hair, what could you infer? In the real world: it's raining outside, I just showered, or maybe someone dumped a bucket of water on my head?? On the GMAT: NONE of those are acceptable. The only thing you can legally infer is that my hair is NOT dry!!

So we are looking at "logical" inference. This means that the correct answer must tie directly to facts in the argument with only slight variations (ie. we can take a look in the negative space: If my hair is wet you can infer (the negative) that my hair is NOT dry).

So for this question, answer choice B makes the most sense:

- From sentence 2, we know that NO TWO kids used the same object as a rolling pin,
- and from sentence 3, we know that each student only identified their own object when asked to find a rolling pin.

So, every child picked a DIFFERENT object to mean rolling pin...
No two children understood the name "rolling pin" to apply to the same object.


Whit

Hi!

I received a PM asking for clarification on a couple of points made as well as some continued advice on dealing with Assumption questions so here goes (I warn you, it isn't short)

David@VeritasPrep wrote:What you call "weakening the premises" are answer choices that "must be false" -- Remember that you cannot weaken premises as premises are facts that you must accept.

Although I agree with David that for the majority of CR problems, the premises are presented as facts (and therefore not open for contention), there are sufficient exceptions to warrant mentioning. In general, premises are any statements, facts OR propositions that form the basis for a conclusion, and GMAT premises can (and do) come in a variety of shapes and sizes. While certainly not as frequently used as "fact" premises, some GMAT arguments do base conclusions on premises that are claims or projections. For this reason, we want to be a bit hesitant to always assume they are facts (and therefore never question or attempt to support them). A fair assumption for a problem might actually do the work of reaffirming or making a "claimy" premise true.

For example,

Question #44 from the Verbal OG Supplement wrote:Bank depositors in the United States are all financially protected against bank failure because the government insures all individuals' bank deposits. An economist argues that this insurance is partly responsible for the high rate of bank failures, since it removes from depositors any financial incentive to find out whether the bank that holds their money is secure against failure. If depositors were more selective, then banks would need to be secure in order to compete for depositors' money.

The economist's argument makes which of the following assumptions?

(a) Bank failures are caused when big borrowers default on loan repayments.
(b) A significant proportion of depositors maintain accounts at several different banks.
(c) The more a depositor has to deposit, the more careful he or she tends to be in selecting a bank.
(d) The difference in the interest rates paid to depositors by different banks is not a significant factor in bank failures.
(e) Potential depositors are able to determine which banks are secure against failure.

The correct answer in this problem actually addresses the premises in the argument; the argument derives its conclusion that depositors are partly to blame because it CLAIMS that depositors SHOULD/COULD be more selective but are CHOOSING not to be. So if I say that they SHOULD be selective, I am assuming that they actually CAN be...answer choice E.

In another example,

Question #111, OG 12th wrote: The difficulty with the proposed high-speed train line is that a used plane can be bought for one-third the price of the train line, and the plane, which is just as fast, can fly anywhere. The train would be a fixed linear system, and we live in a world that is spreading out in all directions and in which consumers choose the free-wheel systems (cars, buses, aircraft), which do not have fixed routes. Thus a sufficient market for the train will not exist.

Which of the following, if true, most severely weakens the argument presented above?

(a) Cars, buses, and planes require the efforts of drivers and pilots to guide them, whereas the train will be guided mechanically.
(b) Cars and buses are not nearly as fast as the high-speed train will be.
(c) Planes are not a free-wheel system because they can fly only between airports, which are less convenient for consumers than the high-speed train's stations would be.
(d) The high-speed train line cannot use currently underutilized train stations in large cities.
(e) For long trips, most people prefer to fly rather than to take ground-level transportation.

In this question, the correct answer (the one that most weakens the argument) is the choice that directly refutes a premise. The argument says that "consumers choose the free-wheel systems (cars, buses, aircraft)" and the winning answer directly states that this is not the case for planes (aircraft). The correct answer, [spoiler]C, states that "Planes are not a free-wheel system..."[/spoiler].

So again, while the "claimy" premise is not nearly as common on the "facty" one, it is still worth noting that they exist and should be watched out for!

But this does bring us back to the original point (regarding assumption questions) - if a choice is WEAKENING a premise, it cannot be an assumption on which the argument relies. A correct assumption needs to make the argument true, so it would, by definition, need to have a strengthening effect.

David@VeritasPrep wrote:Technically you should never be down to two choices that appear to be equally good. Inference questions are all about elimination of those choices that could be false.

I can definitely agree that there will only be ONE completely correct answer, but you might (frequently) find yourself able to eliminate down to 2 answers and then feel stuck between them (I know this happens both to me and my students fairly frequently). In fact, this is actually quite common as the question difficulty increases. A great strategy (from the test writer's perspective) is to begin creating more and more tempting wrong answer choices.

So how do I handle Assumption questions??
(particularly during those scenarios when I find myself down to 2 tempting answers?)

I use a method of negation (we actually call this L.E.N. in our books, or Least Extreme Negation). So let's make sure we understand exactly what is meant by a GMAT assumption. In any argument there are actually TONS of assumptions swimming around, some necessary and some that would just be nice if they were true but aren't essential. Some assumptions are completely basic (if I tell you that Ashwin is 5 ft 10 inches tall, we must assume that my method of measuring is correct, or that my ruler was accurate). These "basic" assumptions are likely what David was talking about when he said that premises stated as facts should be assumed to be true. The GMAT won't ever introduce an assumption that basic (ie. if they give something as a fact, then I promise you we will not see an answer choice that simply states - "Yep, that fact was actually true!")

GMAT assumptions are only of 1 type, however, Those that MUST be true or the argument FAILS!. This is where the game of "Least Extreme" Negation comes in:

If an assumption MUST be true for an argument to hold, then I CANNOT even bend it without destroying the foundation of said argument.

Another example,

Question #63 from the OG Verbal Supplement wrote: Traditionally, decision making by managers that is reasoned step-by-step has been considered preferable to intuitive decision making. However, a recent study found that top managers used intuition significantly more than did most middle- or lower-level managers. This confirms the alternative view that intuition is actually more effective than careful, methodical reasoning.

(D) Top managers use intuitive reasoning in making the majority of their decisions.

(E) Top managers are more effective at decision making than middle- or lower-level managers.

Which answer choice is the better assumption to make?

I have eliminated all of the other (less tempting) choices and left us with the 2 best options. And both sound pretty good, right! So how can we tell?

Let's try to "bend" each choice, and here is what I mean:

Bend (D): "Top managers use intuitive reasoning in making SOME of their decisions." (rather than "the majority")

Well, the argument states that top managers use intuitive reasoning more THAN DO middle and lower level managers. Could this be true if Top Managers are using intuitive reasoning for only SOME of their decisions. Well, they could use it 30% of the time and then middle-low could use it 10% of the time, so I have not really done anything to impact the argument. Hmmmmm....

Bend (E): "Top managers are EQUALLY AS effective at decision making as middle- or lower-level managers." (rather than "more")

Well, the conclusion is that Intuition is more effective, and the basis for that is due to the fact that Top managers use intuition more than low-middle managers. BUT, if top managers are only equally as effective as middle or low level manager, then how can I say that what they are doing (intuition) is better?? I can't! I just "bent" the assumption and "broke" the argument! [spoiler]The correct answer must be E![/spoiler]

Again, keep your negations as slight as possible. For many answer choices, a complete reversal would break the argument, even if the answer wasn't a good assumption choice. The example would be to

BREAK (D) "Top managers use intuitive reasoning in making NONE of their decisions." (a complete and total negation of "the majority")

Well, now what have we done. If we go this far (rather than the slight negation above), then we have made a premise false. How could Top managers use intuition more than anyone if they NEVER use it!?! So breaking this choice actually DID break the argument, but ONLY because I took it too far!! So practice using LEN on questions you already know the answer to for practice. You want to start finding the key places/words/phrases to bend:

• "majority" becomes "some"
  "more than" becomes "the same as"
  "always" becomes "most of the time" rather than "never" (too far)
  "never" becomes "once" or "occasionally" rather than "always" (too far)
  "will" becomes "might"
  "will not" becomes "might not"
  etc...

I hope this gives you yet another tool in your arsenal to help you understand and deal with these tricky assumption questions!


Whit