Logical reasoning PrepTest 141 · Section 2 · Question 21

Incorrect. The stimulus doesn't even guarantee that any student received an A- or higher (just a B- or higher), so this answer isn't supported.

Incorrect. This answer is a reversal of the conditional, which is illegal. (Note that there are some cases where we can reverse a conditional and change it to a some statement, but not a most statement, as this answer choice does.)

Incorrect. Tricky! This answer choice is very close to a correct answer. However, our inference is that most of the Spanish 101 students didn't receive a grade lower than a B-, which leaves open the possibility that they all received a B-. Be careful with negations of lower than/greater than statements, as tricky LSAT answers will play off of that middle ground.

Incorrect. This answer is a weird half-contrapositive, half-negation of the conditional statement. That's not a legal inference.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Spanish 101 student-most-100% attendance
Received lower than B- → not 100% attendance

Answer Anticipation:
A most statement and a conditional can be combined to form an inference, but the sufficient condition of the conditional must be shared. Here, we can make that happen by taking the contrapositive of it:

100% attendance → not Received lower than B-
Spanish 101 student-most-100% attendance

When combining quantified statements to form inferences, the inference is almost always a some statement . . . with one exception. There are certain combinations of most and conditional statements that lead to a most inference (but not all such combinations do). This is an example of that exception.

To see it, think about 100 perfectly representative students in Spanish 101. According to the most statement, at least 51 had 100% attendance, and the conditional tells us all 51 of them didn't receive lower than a B-. In other words, at least 51 of the 100 Spanish 101 students didn't receive lower than a B-, which is most of them:

Spanish 101 student-most-not Received lower than B-

Answer Explanation:
This answer matches the valid inference we anticipated, and it distinguishes itself from (C) by including that B- grade.

Key Takeaway:
Making inferences from quantified statements and conditionals is a skill that is usually tested 1-2 times on the exam. It's not intuitive, but it is memorizable, and so spend some time getting familiar with it to pick up these couple of questions quickly.