Reply To: Eliminating CNBTs in CBT Qs

August 16, 2017 at 3:00 pm #3273

Typically, on a CBT question, you want to find a layout where the answer choice is true; if you find one example, you’re gold. Sometimes, the rules will eliminate the other answer choices, the “MBF” (Must Be False, which I assume is what you mean by CNBT (can not be true?)). It’s usually the case, though, that the reasons that the MBF answers are wrong is somewhat hidden (except on acceptability questions), so generally, I’d be looking for layouts that show that one of the answer choices is possible, although I might scan the choices first and see if I can easily eliminate them (maybe all 4, but not usually).

As for the questions you asked about, the first thing I’d do on the first one is address that ambiguity about “the maximum number of aisles that could separate them,” and as is usually the case, the efficient way to address that is systematically. The theoretical maximum is to put her aisles on the endpoints, but that’s impossible, because of the L rule. So can I move one of them in by just one spot? I can’t give her aisle 2, because that’s Kurt’s aisle. That leaves aisles 1 and 8 for Larissa, and I’d plug that into my diagram:


Actually, I’d work this game with templates relying on the limited possibilities for the MKM block. Because we have to leave room for O and L to follow it, that block can only occupy positions 345, 456, or 567. But let’s say I weren’t using templates. Having placed L and positions 1 and 8, there are now only two places for MKM – 345 or 456 (567 is gone, because there’s no room for the other O, which much come before position 8. Since there are only two possibilities, and each one takes care of half of my remaining variables, I’d plug them both in to examine them on separate tracks. It’s got to be either:


In the bottom one, all that’s missing are two Js, so we can fill them in. In the top one, we’re missing two Js and the O, and the J’s can’t be consecutive, so one of the is in position 9. So it’s:


The first of these layouts matches (A), so we’re done. Notice that the bottom layout also eliminates (A) and (D) on the next question, so I’ve already found two of the wrong answers. I’m always looking to use past layouts to help me on future questions.

Question 5 on PT 56 is more wide-open, so I’d base my work on the answer choices more than the initial setup (there are too many places F could be). So I’d start with (A):

The first rule is already satisfied; wherever we put J, it will come before H. We have:

GL – K
and J and L are separated by 1.
And F can’t be first.

Again, to be systematic, there are only two possibilities – G is first, or L is first. I’d pick one of them and try it. If G is first, L is second, and J is 4th (JL rule):

GL?J?H F and K are interchangeable at this point, so I throw one in there:

I run down my list of rules: J is before H; G is before K; G and L are consecutive; J and L are separated by 1 audition. So (A) is right -If F is not at 1 PM, H COULD BE at 6. Once you find one that works, you’re done.

Sometimes, it’s not hard to pick off the wrong answers on a CBT, but other times, it can be. Usually, I’d spot check the answers, but if I’m not seeing clear, quick, easy ways to eliminate answers, I’m not going to do the deer in the headlights thing; I’m going to grab an answer choice and run with it.