Skip to Main Content

PrepTest 73, Logical Reasoning 2, Question 10


Question 10, when a question asks for the criticism that an argument is most vulnerable to, it's a flaw question, which means that the argument is bad and we have to find out why. And of course before we can find out why, we need to break the argument down into its component parts. This argument comes to us from a vacuum cleaner sales person and their conclusion is actually stated twice.

Basically, the conclusion is that the Super XL is a better vacuum cleaner than your old vacuum cleaner. I don't know if you know that you had a vacuum cleaner, but you do, and it's old. The evidence for their conclusion comes in the middle the demonstration they ran. They ran your old vacuum cleaner over some dirty carpet then they ran the Super XL over the same carpet and the Super XL picked up some dirt that your old vacuum cleaner didn't.

That's why they're saying that the Super XL is the better vacuum cleaner. The flaw in this argument isn't one that's very common on the test. We're very rarely dealing with tricky vacuum cleaner salesmen. But if you use your common sense, you can probably figure it out. The Super XL isn't being judged against the old vacuum cleaner under the same circumstances.

We're comparing the second pass with the Super XL to the first pass with the old vacuum cleaner. Maybe the old vacuum cleaner if the roles were reversed would pick up just as much dirt or more as the Super XL on the second pass. The problem is we're comparing second past and first pass. So let's look at the answer choices to see if anything names that problem.

Answer choice A says that the argument is ignoring the possibility that dirt remained even after the Super XL had been used in the test. This answer choice might seem pretty tempting because it is at least attacking the Super XL, but the argument isn't saying that the Super XL is the perfect vacuum cleaner that gets all possible dirt. Just that it's better at dirt than your old vacuum cleaner.

So the existence of some dirt in the carpet doesn't really matter to the argument. What matters is would the Super XL have done as well if it were used first? So A is not the answer, look at B. B is also pretty tempting. It says that it takes for granted that the Super XL will still perform better than the old vacuum cleaner when it gets old.

This would be the right answer if the argument had been trying to prove that the Super XL was better under all circumstances, but all they said was that it was the better vacuum, better right now versus how your old vacuum is right now. So answer choice B is not our answer. Answer choice C says that the argument takes for granted that because a Super XL did the best at this test, it's the best vacuum cleaner available.

Remember, the argument was only trying to prove that the Super XL was better than your old vacuum cleaner, not that it was the best. Answer choice D then ignores the possibility that the amount of dirt removed from the test by the old vacuum cleaner is greater than the amount of dirt removed by the Super XL. This answer isn't quite right.

The evidence wasn't the Super XL picks up more dirt on the second pass than your vacuum did on the first pass, just that it picks up dirt that your vacuum left behind on the first pass. So it doesn't matter how much was picked up. What matters is that it's picking up dirt that the first vacuum cleaner didn't get, which means that the answer must be answer choice E.

And answer choice E says exactly what we wanted. Ignores the possibility that if the Super XL had been used first, it would have left behind just as much dirt as the original vacuum cleaner. This argument is pointing out that the original test wasn't apples to apples, it was apples to oranges. So answer choice E is what we're looking for and it is our answer.

Read full transcript