Tackling Find the Assumption CR Problems

by on October 16th, 2012

Find the Assumption questions are very common Critical Reasoning question types. If you don’t yet know the general process for tackling Critical Reasoning problems, learn how before you keep reading this article.

Ready to try a question? Set your timer for 2 minutes and try this GMATPrep® problem:

In a study conducted in Canada, servers in various restaurants wrote “Thank you” on randomly selected bills before presenting the bills to their customers. Tips on these bills were an average of three percentage points higher than tips on bills without the message. Therefore, if servers in Canada regularly wrote “Thank you” on restaurant bills, their average income from tips would be significantly higher than it otherwise would have been.

“Which of the following is an assumption on which the argument relies?

“(A) The “Thank you” messages would have the same impact on regular patrons of a restaurant as they would on occasional patrons of the same restaurant.

“(B) Regularly seeing “Thank you” written on their bills would not lead restaurant patrons to revert to their earlier tipping habits.

“(C) The written “Thank you” reminds restaurant patrons that tips constitute a significant part of the income of many food servers.

“(D) The rate at which people tip food servers in Canada does not vary with how expensive a restaurant is.

“(E) Virtually all patrons of the Canadian restaurants in the study who were given a bill with “Thank you” written on it left a larger tip than they otherwise would have.“

Got your answer? Let’s start going through this one!

Step 1: Identify the Question

The question stem contains the word “assumption,” which is a pretty good clue that this is a Find the Assumption (FA) question. This question type always contains a conclusion and I know it’s important to find that conclusion. Also, if I can, I’m going to brainstorm any assumptions I can think of without taking too much time.

Step 2: Deconstruct the Argument

Here, I’ll show you what I’m thinking while I read the argument and also how I would take notes. Your own thought process won’t be exactly the same as mine and, of course, your notes will probably look quite different, since we all have our own ways of abbreviating things.

I’ve thought of a couple of different lines of attack. First, maybe there’s something around the word “significant.” Also, the author is assuming that what happened during the study will continue to happen in future, but maybe there’s some reason why that wouldn’t happen. I can imagine that I might respond by giving a larger tip the first couple of times I saw “Thank you,” thinking the server had taken extra care to write the note… but if everybody did it, it wouldn’t have the same impact.

Note: I’m not really articulating all of the above to myself in so many words – there’s not enough time. But quick ideas or impressions come to us as we read these arguments, and the above would be my general impression for this one.

Step 3: State the Goal

This is an assumption question, so I have to find something the author MUST believe to be true in order to draw this conclusion (that writing “Thank you” on the bill will result in “significantly” greater tips on average).

Work from Wrong to Right

We still have two answers left, B and E, so now we compare them.

Wow, I was pretty convinced when I read answer B, but now that I’ve read E, I think that one is it! Argh.

Okay, answer B addresses the issue of whether there would be an unintended consequence of seeing “Thank you” all the time – if people who see it all the time then start ignoring it and go back to their old tipping habits, then the servers aren’t going to maintain that increase in their tips. Does the argument say that the result (significantly more in tips) would be short-term? No, it implies that this increase would be permanent. It wouldn’t be, though, if people did revert to their old tipping habits, so the author really does have to assume that people won’t go back to their old habits. B is still looking good.

What about E? I still like the fact that this answer says that the “Thank you” people gave larger tips than they otherwise would have. But both answers can’t be right! Is there anything else here? Oh, I think I see. At the beginning, the answer says that “virtually all patrons” gave higher tips. Is it necessary to assume that they all or almost all gave higher tips? Maybe a smaller portion gave much higher tips, and so the overall increase averaged to 3%. Let me just check the conclusion… yes, I’ve got it! The conclusion also just talks about an average increase, so the author is not assuming that everyone gives higher tips – just that some people do.

The correct answer is B.

Also, I’m pretty impressed by that wrong answer E. One part of it is an actual assumption – the author does have to assume that the “Thank you” note did specifically cause the change in behavior. The problem with E was that it went too far in assuming that “virtually all” of the people changed their behavior. That was seriously tricky.

Take-aways for Find the Assumption (FA) CR questions:

(1) Know how to identify the question type. Most FA questions contain some form of the word assume or assumption, though occasionally the question will ask what information is “required” or what information would allow the conclusion to be “more properly drawn.”

(2) Deconstruct the argument according to the goals for this type. FA questions all have conclusions and they all hinge on finding some assumption, so I should be looking for these things as I read the argument. I don’t have endless time to brainstorm assumptions; I’ll have a better shot at thinking of one or two efficiently if I know to think about it while I’m reading the argument for the first time.

(3) Remind yourself of your goal. At first, you may need to say to yourself: “For FA questions, I need to find something that the author must believe to be true in order to draw that conclusion. Some trap answers might involve something the author could believe to be true, but that’s not good enough.” Longer term, you may be able to say to yourself, simply, “Find Assumption” and know what that entails.

(4) Cross off wrong answers first, then worry about finding the right answer. Don’t waste time trying to decide whether B is actually correct when you haven’t looked at C, D, or E yet. Eliminate first, then compare any remaining answers, as we did on this problem. Watch out for traps! On Assumption questions, one common trap answer tells us something that’s reasonable to believe could be true (such as answer C), but the author doesn’t absolutely have to believe that it’s true in order to get to his conclusion. Another common trap is the “irrelevant distinction” trap, where the answer tries to make a distinction between two or more groups or categories, but those distinctions do not actually matter to the given conclusion, as in answers A and D.

* GMATPrep® questions courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.

9 comments

  • I guess we can eliminate E on the basis that in concluding anything about the future we do not have to assume what happened in past. Lets say that E did not have "virtually all". In that case E would be "patrons of the Canadian restaurants in the study who were given a bill with “Thank you” written on it left a larger tip than they otherwise would have". Our conclusion is regarding whether continuously showing "Thank You" would lead to continuous higher tips or not. The new version of E that i mentioned above can strengthen the conclusion but certainly will not be an assumption.

    • Exactly, good - IF answer E were true, then that would strengthen the conclusion. But it does not HAVE to be true, which is required of an assumption. What does have to be true is that at least SOME of those patrons gave a larger tip than they otherwise would have - but not necessarily "virtually all."

  • if we negate answer choice E and check, it does not weaken the argument as strongly as choice B does.. i found the answer using this method.. is it ok?

    • You can use the negation method on Find the Assumption questions, yes! I'll explain for others who might not know what we're talking about.

      The "negation" method means to change the answer in a certain way and we see how that affects the argument - just be careful because the word "negation" makes it sound like you should completely swap it around, but we don't want to do that.

      For answer E, we would say, "Many, but not virtually all, of these customers left a larger tip than they otherwise would have." That doesn't really change anything at all for the conclusion.

      For answer B, we would say, "Regularly seeing "thank you" on the bills would lead many patrons to revert to their previous tipping habits." This actually hurts the argument! If people get used to seeing thank you and stop leaving big tips... there goes the conclusion.

      When you negate, the correct answer should actually make the argument worse. The incorrect answers shouldn't really do much of anything. You don't want to use this technique on all answers because it takes time and it can be tricky / confusing. But if you're stuck between two answers, this can be a very useful technique.

  • Hi stacey, 
    For B to be the correct assumption, we also need to assume that earlier tipping habits means that tips were huge earlier.. 
    Is this correct? Assuming something for the correct assumption answere

    • Not quite - though I think I see what you're getting at. The author states that the overall tip amounts increased for the people in this study (that's a fact) and then he makes a (bad) assumption that continuing that behavior (writing Thank You) will lead to the same result (increased tipping), in general and forever. (He just says this will be the new trend, with no given end date... so he's assuming that writing Thank You will permanently change consumer behavior.)

      Therefore, he's also assuming that the behavior won't go away again for any other reason in future - such as getting used to the "Thank You" and then starting to ignore it.

      We don't need to assume anything else here - we're taking his baseline scenario as a fact (that people in this "Thank You" study really did tip more on average). We're just quibbling with his assumption that this would continue to work in the same way in future if it became a widespread practice. :)

  • I would not dismiss choice "A" just yet as it talks about regular (repeat behavior) vs occasional customers. Regular patrons behaving similar to occasional patrons could mean that presenting the "thank you" bill to a patron on multiple occasion (regular patron) still results in increase in tip amount. The problem does not talk about whether the test was done on just one day or during span of a month or year.

    A is very similar to B actually.

    • There is an important distinction, though. A says that the author needs to assume that two sub-groups (regular and occasional) exhibit the same behavior / response. The argument doesn't require that the subgroups behave in the same way; it only requires that enough people in the overall group behave in a certain way. It could be the case that occasional patrons usually behave completely differently, yet a high-enough percertage of the overall group of patrons still behaves in the required way.

      As I mentioned in the article, this is a common trap they like to set for us - breaking a big group into smaller sub-groups when the sub-groups actually don't change anything or don't matter. Keep an eye out for this one!

  • before, after deconstruct the argument, I try to find out what must be true for the argument to be true. but doing this way, I find hard to find assumption

    if I criticize the argument first, asking questions such as why this, if this thing happen, what happen, I see that I can realize the assumption more easy.

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