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 Post subject: GMAT Verbal Sentence Correction
PostPosted: Mon Apr 23, 2012 4:22 am 

Joined: Tue Nov 27, 2012 7:29 am
Posts: 12
Psychics claim to be gifted with powers that enable them to foretell future events. In the past, psychics have predicted numerous actual events, including the election of President Obama, the stock market crash of 2008, and the Boston Red Sox’s 2007 World Series victory.

The answer to which of the following questions would be most useful in evaluating the validity of the claim that psychics are able to accurately foretell future events?

A. What percentage of psychics’ predictions have come true?
B. Could the election of President Obama have been predicted without the help of psychic powers?
C. What is the actual mechanism by which these psychic powers are alleged to operate?
D. How long before the events in question do psychics make their accurate predictions?
E. Do most scientists accept the idea that the power to predict the future through psychic means really exists?

(A) The passage cites just three accurate predictions by psychics and alludes to others. However, the existence of three successful predictions is not sufficient to prove the existence of psychic powers. To evaluate whether psychics can accurately predict the future, one needs to know what percentage of psychic predictions have been accurate. A success rate of 95 percent might legitimize the possibility of psychic talent, while a success rate of 5 percent might suggest that the psychic is a fraud.
Choice (E) isn’t directly relevant to the issue of psychic abilities being valid.
Answering the questions in choices (B) through (D) will not garner evidence in support of the psychic success rate, leaving (A) as the correct answer.


Assuming the psychics got 4 out of 5 predictions right, it is still only 4 and does not indicate consistency of successful predictions over the long haul.

Given the above, I strongly feel that the answer has to be option D since, you can have events for which ominous/good signs begin appearing a few days before its occurrence and this is publicly known. If this is the case then the psychic ability comes into question doesn't it ?

 Post subject: Re: GMAT Verbal Sentence Correction
PostPosted: Mon Apr 23, 2012 4:24 am 

Joined: Mon Feb 27, 2012 8:22 pm
Posts: 26
Choice (A) does not imply a small sample size. In fact, it talks about the accuracy percentage for all psychics' predictions. Your rationale for choice (D) would only be valid if all events had some form of warning sign before their occurrence, but this is demonstrably not the case for many events. For example, there is no prediction system for earthquakes, so knowing that a psychic predicted an earthquake one day or one century before it occurred would tell you nothing about their ability; in either case it could have been luck. Conversely, if you knew that psychics have accurately predicted 95% of all earthquakes, that would be powerful evidence of their talent.

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