0

# CR Tutorial Inference

Inference Questions (CR)

When dealing with Critical Reasoning questions, you can often see an Inference question.

The following are some of the possible question stems of Inference questions.

Which one of the following can be properly inferred from the argument above?

If each of the statements above is true, which of the following must also be true?

Arguments accompanying Inference questions do not, as a rule, have a conclusion and are just a list of premises or factual information; however some of these arguments may have a conclusion.

To properly answer an Inference question you have to find an answer choice that must be true based on the information provided in the argument. Correct answers to these questions never provide any new information or change the logic of an argument; they are inferred from the argument itself. When dealing with these questions, do not make any assumptions of your own; the answer must be true based solely on the information provided in the argument. Eliminate answer choices that may or may not be true based on the evidence provided in the argument. Also eliminate answer choices which restate or rephrase premises of the argument at hand.

Examples:

Evidence: People under the age of 13 are not allowed to take the GMAT. Jason is now 10 years old.

Inference: Jason is not allowed to take the GMAT.

Incorrect Inferences: Jason will take the GMAT in three years; it is unfair that people under the age of 13 cannot take the GMAT.

This is a very basic example just for you to see what a correct inference may look like. If Jason is 10 and people under the age of 13 are not allowed to take the GMAT, then it must be true that Jason is not allowed to take the GMAT. This inference is based solely on the information provided in the stimulus and adds no “outside” information. It does not restate premises but is based on (inferred from) them.

The examples of incorrect inferences either require additional evidence or are out of scope. We need more information to infer that “Jason will take the GMAT in three years”, since the evidence itself does not provide any grounds for such an inference. “It is unfair that people under the age of 13 cannot take the GMAT” – the evidence provides no information to judge whether this GMAT policy is fair or unfair.

Consider the following example of a harder inference question:

Increased production costs often cause companies to increase prices on their products. Next month, InterGaz Company, which supplies natural gas to all manufacturers in Cantalia, will increase gas prices by 20%. This will ultimately result in increased production costs of Cantalian car manufacturers, since their production costs greatly depend on natural gas prices.

Which of the following can be properly inferred based on the information above?

-    After gas prices are increased, Cantalian car manufacturers will increase prices on their products.

-    After gas prices are increased, production costs of Cantalian car manufacturers will increase by 20 percent.

-    After gas prices are increased, some Cantalian car manufacturers will be forced out of business.

-    After gas prices are increased, Cantalian car manufacturers are likely to increase prices on their products.

-    After gas prices are increased, profits of most Cantalian companies which purchase natural gas from InterGaz are going to decrease.

Explanation: Let’s simplify our argument and leave only factual information:

-    Increased production costs often result in increased prices.

-    Next month, gas supplied to all manufacturers in Cantalia will get more expensive.

-    Production costs of Cantalian car manufacturers will increase.

Now let’s analyze answer choices one by one to see which one must be true based on this information:

(A)   “Cantalian car manufacturers will increase prices on their products”. The word “will” in this choice is an “extreme” word. We were told that companies “often” (not “always”) increase prices when production costs increase. Therefore, we do not know for sure whether the prices “will” be increased. This can possibly be one of those cases when selling prices do not change even though production costs have increased.

(B)   This would be true only if gas prices were the only factor that determines production costs of Cantalian car manufacturers and we don’t know if this is so.

(C)   This answer is ungrounded and even though it may be true, nothing in the argument proves it to be true.

(D)   Correct. If increased production costs often cause companies to increase prices of their products and production costs of Cantalian car manufacturers will increase, then they are likely to increase prices on their products. This choice is much like A but it uses a the more appropriate words “are likely”, which are quite compatible with the word “often” used in the argument, instead of the extreme word “will” used in choice A.

(E)   We have no information about profits, thus this statement is out of scope. Production costs is only one factor which determines profits, and knowing only this one factor is not sufficient to conclude about how the profits of those companies will change.

Traps in Inference and Conclusion questions

When dealing with Inference and Conclusion questions pay attention to:

“Extreme words” If the evidence is about “some” you cannot infer or conclude about “all” or “most”.

Example:

Evidence: Some students of Eastlake High have cars. Jason is a student of Eastlake High.

Wrong Inference or Conclusion: Jason “has” a car.

Correct Inference: It “is possible” that Jason has a car.

The wrong inference uses an extreme word “has” a car, while from the evidence we know that only “some” students of Eastlake High have cars and it is possible that Jason is among those students who don’t have cars. This inference may (but does not have to) be true, and therefore is incorrect.

The correct inference says that “it is possible” that Jason has a car and thus considers both possibilities:

1. Jason is among those Eastlake students who have cars

2. Jason is among those Eastlake students who don’t have cars.

Necessary vs. Sufficient

Remember not to confuse what is necessary for something to be true with what is sufficient for something to be true.

Example:

Evidence: All adults have certain responsibilities. Jason has certain responsibilities.

Wrong Inference: Jason is an adult.

Correct Inference: People who do not have any responsibilities are not adults. It is possible that Jason is an adult.

The wrong inference confuses what is necessary to be an adult with what is sufficient to be an adult. The evidence that all adults have responsibilities does not eliminate the possibility that other people, for example children, have responsibilities. Therefore, having responsibilities is necessary but not sufficient to be an adult. And it is possible that Jason is a child.

The correct inference “People who do not have any responsibilities are not adults” states that it is necessary to have responsibilities to be an adult and that is true based on the evidence.

It is possible that Jason is an adult” is also true; since Jason meets a necessary condition stated in the evidence, it is possible that he is an adult.

Example:

Evidence: All adults have certain responsibilities. Jason also has responsibilities.

Wrong Inference: Jason is an adult.

Correct Inference: People who do not have any responsibilities are not adults. It is possible that Jason is an adult.

If you negate the wrong answer, you get “Jason is not an adult” This is quite compatible with the evidence. All we know is that Jason has responsibilities which is necessary, but not sufficient, to prove that his is an adult and thus it is possible that he is not an adult. As you can see, negating  the wrong inference resulted in a statement that is quite compatible with the evidence.

Now try to negate the correct answer. This gives you: “People who do not have any responsibilities are not adults”. This negated statement directly contradicts what was stated in the evidence: “adults have responsibilities”.

Negating the second correct inference results in “It is not possible that Jason is an adult”. This also contradicts the evidence. It was stated that Jason and adults have responsibilities. Therefore it is possible that he is an adult.

Negating the correct answer results in a statement that contradicts the evidence.

Tips for Inference Questions:

1. Choose an answer choice that must be true based on the evidence presented.

2. A correct answer to an Inference question does not present any “outside” information; it is based solely on the information provided in the argument.

3. Be careful with answer choices that use extreme language. When you see “extreme” words make sure their use is logical.

4. If not sure, check the selected answer by negating it.

Notes from Himang Jain