At Food World Supermarket, built in 1975, the number of successful

Question

At Food World Supermarket, built in 1975, the number of successful thefts has risen dramatically in the last few months. Food world has a reliable electronic security system at all the customer exit doors, and this system is always operational. Therefore the thefts must have been committed by people who used exits other than the regular customer exit doors.

Which of the following is assumption that would make the conclusion above logically correct ?

(A) If a surveillance system is installed in a supermarket, it is always equipped at every possible exit.

(B) If an employee so wishes, he is allowed to leave thorugh an exit that is not monitored by surveillance system.

(C) If a store has reliable security system, it is impossible to pass through the system undetected.

(D) If a supermarket was built before 1980, it often has exits that cannot be equipped with electtronic surveillance.

(E) If a store has a reliable electronic security system but is still experiencing a rise in theft, it must be the case that the employees must are stealing.

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BongBideshini · Answer

A. If a surveillance system is installed in a supermarket, it is always equipped at every possible exit.  
This choice should be eliminated because it actually hurts the author's logic rather than helping it. 
 
B. If an employee so wishes, he is allowed to leave through an exit that is not monitored by the surveillance system.  
 Knowing that employees are allowed to use unmonitored doors does not prove that the thieves actually used those doors.

C. If a store has a reliable security system, it is impossible to pass through the system undetected.  
If it is completely impossible to pass through a reliable system undetected, and the main customer doors have a reliable system, then we can confidently eliminate the main doors as a possibility. This forces the thefts to have occurred at the other exits, making the author's conclusion logically certain.
 Correct

D. If a supermarket was built before 1980, it often has exits that cannot be equipped with electronic surveillance.  
Proving that other exits exist is not the same as proving that the thieves actually used them.

E. If a store has a reliable electronic security system but is still experiencing a rise in theft, it must be the case that the employees must are stealing.  
This choice is incorrect because it introduces the identity of the thieves rather than addressing the physical path of the theft. 
 Ans C

arushi118 · Answer

Correct Answer: C 
The argument assumes that the electronic security system would detect anyone who passed through the monitored customer exits.

(A) Doesn't guarantee that a thief using the customer exit would be detected.
(B) Talks only about employees, not all thieves.
(D) Says other exits may exist, but doesn't prove thieves used them.
(E) Changes the conclusion to "employees are stealing," which is not the argument's conclusion.

Bunuel · Answer

Official Explanation

This is an Assumption question. The correct choice will be something the author left out, but must believe to be true for the conclusion to follow from the evidence. The author's conclusion comes after the conclusion keyword, "therefore." The thefts must have been committed by people using other exits. As evidence, the author notes that Food World has a reliable electronic security system at all customer exit doors. This system is always in operation. Note the extreme language in the conclusion - the thefts "must" have been committed by people using other exits. Whenever the conclusion contains definite language like this, consider whether the author has gone too far. Here, the security system is "reliable." This doesn't mean it's infallible, or that there is no way to get past it. In order to conclude that the thefts must have gone through other exits, however, the author must be assuming the system is indeed infallible and that there is no way past it.

(C) matches this prediction and is the correct answer. If the author thought it was possible to pass through the system undetected, he wouldn't conclude the thefts must have gone through other exits. Thus, the author must believe it is impossible to pass through the system undetected.

(A) can't be assumed by the author, because he concludes that the thefts took place at exits that did not have the system. It would contradict his argument if the author believed that every store with a system has the system on every possible exit.

(B) wouldn't make the conclusion correct, because the author already concludes that the perpetrators are using exits that are not monitored. Whether the perpetrators are employees or not is irrelevant. The argument is simply that, from the fact that there is a reliable security system at all customer exit doors, the thefts must be occurring through other doors. (B) doesn't deal with the connection between those two things.

(D) is irrelevant to the argument, since the stimulus already states that Food World has some exits that don't have the security system. Whether or not those exits could be equipped with "electronic surveillance" (which isn't even necessarily the same thing as an "electronic security system") is not important to the reasoning.

(E), if assumed, would not make the conclusion that the thefts were being perpetrated through certain exits correct. Even if it were known that employees were the thieves, the employees could be using customer exits and somehow bypassing the security system.

TAKEAWAY: Be very clear on the evidence and conclusion of the argument, and stick to the connection between them. Irrelevant choices are quite common, and can be easily spotted by having a good paraphrase of the argument.

At Food World Supermarket, built in 1975, the number of successful

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