DS: Yes/N0 3-Step Test

[mrkamal]

If you misinterpret a question to be a fraction vs. integer type and it is not, will you always get the answer wrong using the FIZ test? I made that mistake and got the answer wrong, so I know it's wrong at least some of the time.
Thanks

[esledge]

Yes, you often will get the wrong answer, although not necessarily every time.

For example, if you mis-categorize a positive/negative question as a fraction/integer question, and thus use FIZ (fractions, integers, zero) instead of NPZ (negative, positive, zero) as a reminder of the values to check, you could very well miss something--namely, by not checking a negative value. Maybe that negative case would affect the answer, or maybe you get lucky and it wouldn't. But luck really shouldn't be a factor in your GMAT preparation!

So, I think there might be a question behind your question--If the NPZ, FIZ, etc. mnemonic devices exist to tell you what values to check, how do you CORRECTLY decide which one applies to a particular question?

I have a recommendation that I believe will help you, but we would need a problem to use for the discussion. Can you post (to this thread, with citation of source) the particular problem you mentioned?

Thanks,

[mrkamal]

Thanks Emily.
The question I was referring to was in Lab #2. It is listed on the slide as 183 (must be from 10th Ed. because it's not in my book). It asks if x squared is greater than x?
Best,
AK

[esledge]

Yes, that is DS#183 from the OG 10th edition. The same problem appears in the Official Guide for Quant Review (11th ed.) as DS#78. Here it is for the record:

Is x^2 greater than x?
(1) x^2 is greater than 1.
(2) x is greater than -1.

This problem is actually testing more than one thing.

It is testing fractions vs. integers because it asks you to compare x^2 to x^1, and proper fractions get smaller when squared (e.g. (1/2)^2 = 1/4, a smaller value than 1/2). In contrast, integers (and larger fractions such as 3/2) get larger when squared (e.g. 2^2 = 4, a larger value than 2). Thus, you should use FIZ to remind you to test fractions, integers, and zero values.

It is testing positives vs. negatives, too, because one of the expressions has an even exponent. Even exponents "hide the sign" of the base: (-10)^2 = (10)^2 = 100. Thus, you should use NPZ to remind you to test negative, positive, and zero values.

Here are some general suggestions to ensure you don’t miss testing certain scenarios on DS Yes/No questions. Either of these might help; you don’t necessarily need to do both for a given problem:

Suggestion #1: When in doubt, use both NPZ and FIZ. This covers all of the bases: negative and positive fractions, negative and positive integers, as well as zero. Also, consider both proper fractions (e.g. 1/2) and improper fractions (e.g. 3/2).

Suggestion #2: In this problem, instead of starting by generating the possible x values, you could start by generating a list for whatever expression is mentioned in the statements. For example, statement (1) tells us that x^2 > 1. So, you would make a list of possible values for x^2: {x^2: 2, 3, 4, 5, 6, etc.} Only then would you take the square root to solve for the possible values of x: {x: +/- sqrt(2), +/-sqrt(3), +2, -2, +/-sqrt(5), etc.). Doing so would give you a chance to catch the negative possibilities for x, which I believe you missed the first time around.

I hope this helps. Best regards,

[mrkamal]

Thanks for clarifying everything.
-AK