to the top

#2 - People who are red/green color-blind cannot distinguish

PowerScore Staff
PowerScore Staff
Posts: 6670
Joined: Wed Feb 02, 2011 4:19 pm
Points: 3,343

Complete Question Explanation

Parallel Reasoning-SN. The correct answer choice is (B)

The reasoning in the stimulus is a Mistaken Reversal:

    RGC = Red/green color-blind ..... ..... D = Distinguish

    Premise 1: ..... RGC ..... :arrow: ..... D

    Premise 2: ..... DG

    Conclusion: ..... RGCG

Of course, when drawn out together, the Mistaken Reversal is easier to see:

    Premise 1: ..... RGC ..... :arrow: ..... D

    Premise 2 + Conclusion: ..... DG ..... :arrow: ..... RGCG

Note that different people will represent the conditions with different symbology (this is perfectly acceptable). For example, you can diagram the phrase “not distinguish” as ND or D with a slash over it. Either will work to represent the condition. The important thing for you to remember is that once you begin with a certain symbolization y need to continue using that same symbol within the problem and refrain from introducing new ways of representing the same ideas. (We use the D with a slash to represent this since technically that is the most efficient. Using ND ultimately produces ND with a slash which is difficult for most students to work with because it is a double-negative.)

Note also that we have symbolized Gerald as a subscript, and not as a separate condition. Why? Because Gerald is simply a person experiencing one of the conditions; Gerald is not a separate condition unto himself. When a person, place, or thing experiences a condition, simply note that occurrence as a subscript of the original condition.

The question stem requires you to select an answer choice with reasoning similar to the reasoning in the stimulus. Thus, you must find the answer choice that contains a Mistaken Reversal.

Answer choice (A): This answer contains a Repeat form (or restatement form), which is a valid form of reasoning. In these cases, a conditional statement is made, and then a premise is added indicating that the sufficient condition has been met. On that basis, one can infer that the necessary condition must occur. In this problem, the argument appears as follows:

    Premise 1: ..... Fair Skin ..... :arrow: ..... Sun

    Premise 2: ..... Fair SkinW

    Conclusion: ..... SunW

Combined, you can easily see why this is called the Repeat form:

    Premise 1: ..... Fair Skin ..... :arrow: ..... Sun

    Premise 2 + Conclusion: ..... Fair SkinW ..... :arrow: ..... SunW

As this form of reasoning is not a Mistaken Reversal, this answer choice is incorrect.

Answer choice (B): This is the correct answer choice. Similar to the stimulus, this answer contains a Mistaken Reversal:

    Premise 1: ..... Sinusitis ..... :arrow: ..... Lose Smell

    Premise 2: ..... Lose SmellM

    Conclusion: ..... SinusitisM

Again, the Reversal is evident when all statements are combined:

    Premise 1: ..... Sinusitis ..... :arrow: ..... Lose Smell

    Premise 2 + Conclusion: ..... Lose SmellM ..... :arrow: ..... SinusitisM

Note that the terms reverse just as they did in the stimulus. To some students, however, this answer does not appear exactly as the stimulus because there are no slashes present on the necessary term in the first premise and the term in the second premise. Is this a problem? No. We could easily have made the necessary condition diagram as:

    ..... ..... ..... ..... Smell

Had we chosen this representation, then the diagrams would look identical. The key here is that you are paralleling the action (which is a Mistaken Reversal) not the placement of negatives (which can be easily manipulated).

Answer choice (C): This answer choice contains a contrapositive:

    Premise 1: ..... Jaundice ..... :arrow: ..... Blood Donor

    Premise 2 + Conclusion: ..... Blood DonorJ ..... :arrow: ..... JaundiceJ

Note how in a contrapositive, which is a valid form of reasoning, the terms both reverse and negate.

Answer choice (D): This answer choice is another restatement or Repeat form like answer choice (A):

    Premise 1: ..... Color Blind ..... :arrow: ..... Airline Pilot

    Premise 2 + Conclusion: ..... Color BlindA ..... :arrow: ..... Airline PilotA

This answer is also suspicious because it is of the same topic as the stimulus. On the LSAT, in Parallel Reasoning questions answers with the same subject matter as the stimulus are normally incorrect (because you are paralleling the reasoning, not the subject matter).

Answer choice (E): The first sentence of this answer choice appears similar to all the prior answers and the stimulus. The third sentence then appears to start a Repeat form. However, the third sentence of this answer then introduces a new, third term “special diet.” As this answer does not contain a Mistaken Reversal, this answer choice is incorrect.