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Similar reasoning

by BTGmoderatorRO » Sat Oct 07, 2017 12:27 pm
If Joan was growing marijuana plants in her home, she would not allow police investigators to search her home without a warrant. As a result, allowing the police to search her home without a warrant shows that Joan does not grow marijuana plants in her home.

Which one of the following contains an argument logically most similar to the argument presented in the passage?

(A) If Justin were playing golf at the city golf course, he would not be home until dinner. Therefore, the fact that he gets home by mid-afternoon shows that he is not playing golf at the city course.
(B) If Paul were stingy, he would not buy Dorian a birthday present. Therefore, Paul's buying Francis a birthday present shows that he is stingy.
(C) If Jason were over 30, he would not want to listen to rap music. Therefore, the fact that Jason does not like to listen to rap music shows that he is over 30.
(D) If Sandra were a good seamstress, she would not buy cheap fabric. Therefore, the fact that Sandra is not a good seamstress shows that she bought cheap fabric.
(E) If Kevin were hungry, he would not skip breakfast. Therefore, the fact that Kevin is hungry shows that he did not skip breakfast.

OA is a.
What's the best approach to determine the answer? :shock: :x
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by VJesus12 » Sat Oct 14, 2017 6:57 am
Interesting question.

What about option C? It is logically similar to the passage. Isn't it?
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by EconomistGMATTutor » Wed Oct 18, 2017 1:30 pm
This is an IF-THEN argument. If Joan grows marijuana, THEN she would not allow the warrantless search. That's the evidence.

If Joan DOES the allow the warrantless search, THEN she does not grow marijuana plants in her home. That's the conclusion.

That's right. Given an IF A, THEN B statement, one can conclude IF NOT B, THEN NOT A. For example, if you say IF you went to college THEN you went to high school, you can also conclude that IF you did not go to high school THEN you did not go to college. You cannot say IF NOT A THEN NOT B or IF B, THEN A. Only IF NOT B, THEN NOT A can be concluded. This is known as the contrapositive of the original statement. The if-then terms are reversed and negated.

Choice C was asked about. This choice says IF Jason were over 30, THEN he would not want to listen to rap music. But then the author concludes IF Jason does not like to listen to rap music THEN he is over 30. This is like saying IF A THEN B allows us to conclude IF B THEN A. The terms have been reversed but not negated. This is flawed reasoning. The argument does not use flawed reasoning.

I'm available if you'd like any follow up.
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