A new electronic security system will only allow a single person at a

Official Explanation

STEP 1: IDENTIFY THE QUESTION TYPE

Since the stem asks you to accept the statements as true and draw a conclusion on the basis of them, this is an Inference question.

STEP 2: UNTANGLE THE STIMULUS

When untangling the stimulus of an Inference question, briefly paraphrase the important facts to ensure you understand them. The stimulus tells you that a new electronic security system is completely fail-safe and will never allow an unauthorized person through a door equipped with the system. The system allows an authorized person to enter solely on the basis of the person’s appearance and facial features.

STEP 3: PREDICT THE ANSWER

Attempting to predict the correct inference is difficult here, but on the GMAT, remember that an inference is something that must be true, not just something that could or might be true. It’s crucial to approach the answer choices with this definition in mind.

STEP 4: EVALUATE THE CHOICES

(A) is unsupported. There is no evidence of how the security industry is going to respond to the new system, so you can’t say that this statement must be true based on what the stimulus states.

(B) also doesn’t need to be true. The new system doesn’t need to differentiate between people passing by the door and people trying to enter, so long as it lets authorized people in and keeps unauthorized people out.

(C) is too extreme. According to the stimulus, the security system examines multiple facial features to determine identity. You don’t know that any one feature cannot be the same. All you know is that all of the features can’t be the same.

As for (D), the stimulus only discusses the likelihood that unauthorized people will be able to get past the security system and through a secure door; there is no support for a statement about costs.

That means the correct inference must be (E): if one twin is authorized and the other isn’t, you know the system must be able to tell them apart, because the stimulus states that the security system never fails.

Answer: E