Vacuum cleaner salesperson: To prove that | LSAT 73, Q10, LSATHacks

LR Question 10 Explanation, by LSATHacks

QUESTION TEXT: Vacuum cleaner salesperson: To prove that this Super X…

QUESTION TYPE: Flawed Reasoning

CONCLUSION: This super XL is better than this old vacuum cleaner.

REASONING: The salesman ran both vacuums over the carpet. The super XL went second, and picked up dirt. That was dirt the old vacuum didn’t pick up.

ANALYSIS: Door-to-door salesman….does that still exist? Regardless, this is a good trick. The salesman’s argument seems convincing.

But normally, when vacuuming, you make multiple passes. You never pick up all the dirt. It’s possible that if the salesman had run the old vacuum second, it would also have picked up dirt left behind by the Super XL.

For a proper comparison, you need to compare the same thing: The first pass of the old vacuum cleaner on a dirty carpet vs. the first pass of the Super XL on another section of dirty carpet.

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1. This sounds good, but you must take it at its weakest. “Dirt remained” could refer to a very, very tiny amount of dirt. No vacuum cleaner ever picks up 100% of dirt.
2. The salesman wasn’t saying “this Super XL will be better in five years”. He’s saying it is better now. The future state of the Super XL isn’t relevant to a comparison of its present quality.
3. The author didn’t say the Super XL is the best. They just said it’s better than the old vacuum cleaner.
4. Think about how vacuum cleaners work. On the first pass, they always pick up the most dirt. So a worse vacuum cleaner might pick up more dirt if it went first.
   You need to compare apples to apples: First pass to first pass.
5. CORRECT. The salesman didn’t make a good comparison. The first pass of a vacuum cleaner never picks up all the dirt. The salesman should have compared how much dirt each vacuum cleaner would pick up on the first pass.