Logical Reasoning · Flaw

PrepTest 110 · Section 2 · Question 9

Phase 1 (your first ~400 questions): read the guidance, then answer. No clock.

Step 1 · Pre-Question Guidance · read this first

Question type

Flaw

The one idea it tests

A difference in how two reports were made does not, all by itself, explain why their results disagree.

The basic logic

Two sources give opposite results. The argument points to one difference between them and declares the mystery solved. Ask: could that difference exist and the results still match? If yes, the difference alone is not a full explanation.

Tiny words that decide it

“thus”
“no need”
“different”

Playground logic

Marcus and Priya got two different recess times (patty: they used two different watches). Marcus slams the top bun down: 'Different watches, case closed!' The secret sauce is that different tools must give different answers, but two different watches can show the exact same time.

Step 2 · The kid story

The Case of the Two Watches

Marcus and Priya both timed recess on Friday. Marcus says recess lasted 20 minutes. Priya says 30. Lulu, clipboard ready, asks why. Marcus taps his wrist. 'Easy, detective work. I used my dinosaur watch. Priya used her mom's old phone. Different gadgets! Mystery solved. Nobody needs to think about this anymore.' Priya sips her juice box. 'Marcus, my phone and your watch both said 10:15 when the bell rang. Two different gadgets can show the very same time. So the gadgets being different does not tell us why our numbers are ten minutes apart. Maybe one of us started late. Maybe somebody's battery died.' Lulu writes: 'Different tools is not the same as different answers.' Marcus frowns, then checks his watch. It is stuck at 10:35.

Step 3 · Try the model question

Marcus timed recess at 20 minutes. Priya timed it at 30 minutes. Marcus used a wristwatch, while Priya used a phone. So the gap between their times is fully explained, and there is nothing more to look into.

Which choice best describes a weakness in Marcus's reasoning?

Step 4 · The courtroom tale

Two Rulers, One Fence

Two surveyors measured the same garden fence. One said 40 feet, the other said 55. Mr. Whitfield snapped his suspenders. 'Your Honor, one used a tape, the other a laser. Different tools, different numbers. We can all go home.' Judge Okafor raised an eyebrow. 'Counselor, my tape and my laser both measure my desk at five feet. Different tools agree all the time. Telling me the tools differ does not tell me why the numbers differ by fifteen feet. Did someone measure the wrong fence? Start at the wrong post?' Mr. Whitfield sat down slowly. 'I may need a longer lunch break, Your Honor.'

Step 5 · Work the real question

Open PrepTest 110, Section 2, Question 9 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Find the two results that clash and the single difference the arguer offers as the full explanation. Notice the claim that no more digging is needed. Ask yourself whether that difference could exist while the results still matched. Then look for the choice that points out that a difference in approach does not guarantee a difference in outcome.