It is commonly believed that a persons level of intelligence is

­Heres my take.­

It is commonly believed that a person’s level of intelligence is relatively fixed. However, a recent study has demonstrated that doing intensive cognitive training can cause people’s levels of intelligence to increase significantly. Study participants who took a group of tests of intelligence before and after doing intensive cognitive training scored significantly higher on the tests after they did the training than they had before doing it.

Analyzing the passage, we see that it presents an argument with the following conclusion:

a recent study has demonstrated that doing intensive cognitive training can cause people’s levels of intelligence to increase significantly

The support for the conclusion is the following:

Study participants who took a group of tests of intelligence before and after doing intensive cognitive training scored significantly higher on the tests after they did the training than they had before doing it.

We see that the author has reasoned that, since study participants who did intensive cognitive training scored significantly higher on tests of intelligence than they had before the training, the study demonstrates that intensive cognitive training causes people's level of intelligence to increase significantly.

The above reasoning involves which of the following assumptions?

The correct answer will state an assumption that the author has made in arriving at the conclusion.

(A) The study participants’ scores on the tests of intelligence did not increase by much different percentages on different tests.

This choice is not necessary for the argument to work.

After all, even if the study participants’ scores on the tests of intelligence did increase by much different percentages on different tests, the scores still increased. So, the support for the conclusion remains essentially the same even if this choice is not true.

Eliminate.

(B) People’s scores on tests of intelligence usually increase at most insignificantly as a result of their repeatedly taking tests of intelligence.

To analyze this choice, let's consider what happens to the argument if this choice is not true.

If this choice is not true, then people's scores on tests of intelligence usually increase more than "insignificantly" as a result of their repeatedly taking tests of intelligence.

In other words, if this choice is not true, then peoples scores usually increase significantly as a result of their repeatedly taking tests of intelligence.

In that case, it could be that the participants' scores increased not because they did intensive cognitive training but because they repeatedly "took ... tests of intelligence" for the study.

We see that, if this choice is not true, then the fact that the participants' scores increased does not effectively support the conclusion that "a recent study has demonstrated that doing intensive cognitive training can cause people’s levels of intelligence to increase significantly." After all, repeatedly taking the tests rather than the cognitive training may have been what caused the significant score increases.

In other words, for the evidence about the cognitive training and test scores to effectively support the conclusion, the possibility that repeatedly taking the tests of intelligence is what caused the increases must be eliminated.

So, for the argument to work, this choice must be true.

Keep.

(C) What is commonly believed about people’s levels of intelligence is significantly different from the truth about people’s levels of intelligence.

This choice follows from what the argument says. After all, if it is commonly believed that a person’s level of intelligence is relatively fixed, but a recent study has demonstrated that doing intensive cognitive training can cause people’s levels of intelligence to increase significantly, then what is commonly believed about people’s levels of intelligence is significantly different from the truth about people’s levels of intelligence.

So, this choice is not an assumption the argument involves. Rather, it's a conclusion supported by the passage.

In other words, the author does not assume what this choice says. The author makes statements that support what this choice says.

Eliminate.

(D) The study participants had not been successful in increasing their levels of intelligence before doing the cognitive training involved in the study.

Notice that, regardless of whether the study participants had been successful in increasing their levels of intelligence before doing the cognitive training involved in the study, the test results indicate that their levels of intelligence increased when they did the cognitive training.

So, regardless of what occurred before, it appears that, by doing cognitive training, they increased their levels of intelligence.

In other words, even if they increased their levels of intelligence before or in another way, it appears that, by doing cognitive training, they increased them again.

This choice does slightly strengthen the argument by showing that, without doing cogntiive training, the participants did not increase their levels of intelligence.

At the same time, the argument does not depend on this choice being true.

Eliminate.

(E) Most people are sufficiently motivated to increase their levels of intelligence to do the type of intensive cognitive training done by the study participants.

To eliminate this choice, we need to notice that the conclusion of the argument is about what cognitive training "can" do, rather than about what people will do.

Arriving at the conclusion about what cognitive training can do doesn't require assuming what this choice says. After all, regardless of whether most people are sufficiently motivated to do such training, it could still be that it can cause people's levels of intelligence to increase if they do it.

Simply put, what cognitive training can do and what most people are motivated to do are two different things.

Eliminate.

Correct answer: B­­­­­­

Is there a way to improve intelligence? If so, I definitely need this cognitive training, haha.

Well, GMAT prep results in improved reasoning skills. So, there's one possible approach.