LSAT Explanation PT 20, S4, Q11: John works five days each week

LSAT Question Stem

Which one of the following is an assumption on which the argument depends? 

Logical Reasoning Question Type

This is a Necessary Assumption question. 

Correct Answer

The correct answer to this question is D. 

LSAT Question Complete Explanation

The question type for this problem is Necessary Assumption, and we are asked to identify an assumption on which the argument depends.

First, let's summarize and analyze the argument in the passage:

Premise 1: John works five days each week except when on vacation or during weeks in which national holidays occur.

Premise 2: Four days a week he works in an insurance company; on Fridays he works as a blacksmith.

Premise 3: Last week there were no holidays, and John was not on vacation.

Conclusion: John must have worked in the insurance company on Monday, Tuesday, Wednesday, and Thursday last week.

Now let's discuss each answer choice:

a) John never takes a vacation of more than one week in length.

This answer choice is irrelevant because we know that John was not on vacation last week. Whether he takes vacations longer than one week does not affect the argument.

b) Every day last week that John worked, he worked for an entire workday.

This answer choice is not a necessary assumption because the argument is only concerned with which days John worked, not the duration of his workday.

c) John does not take vacations in weeks in which national holidays occur.

This answer choice is also irrelevant because we know that there were no holidays or vacations last week. The relationship between vacations and holidays does not affect the argument.

d) Last week John worked neither on Saturday nor on Sunday.

This is the correct answer choice. Without this assumption, it is possible that John worked on days other than Monday through Thursday, which would weaken the conclusion.

e) There were no days last week on which John both worked in the insurance company and also worked as a blacksmith.

This answer choice is not a necessary assumption because even if John worked both jobs on one day, it would still be consistent with the premises that he worked at the insurance company on Monday through Thursday and as a blacksmith on Friday.

Evaluate Question: "Did John work on Saturday or Sunday last week?" If the answer is "no," then the conclusion is valid. If the answer is "yes," then the conclusion is not valid.

In conclusion, the correct answer choice is (d): Last week John worked neither on Saturday nor on Sunday.