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I had a real problem with this one last night, it seemed pretty cut and dry to me.

Given: Your WLAN equipment operates in a regulatory domain that permits channels 1-13, but not 14, in the 2.4 GHz ISM band. All 5 GHz channels within the range of 5.15 to 5.725 GHz are also permitted.

What is the maximum number of non-overlapping (based on the 802.11 definition) 20 MHz channels that can be utilized by your APs? (Choose 2)

I correctly answered that there were 3 non-overlapping channels in the 2.4GHz range, but my answer of 23 channels in the 5GHz range was marked wrong. Even the explanation text seemed to confirm my answer

UNII-1 :4
UNII-2: 4
UNII-2e:11
UNII-3:4
4+4+11+4=23, however the test engine indicated that the correct answer was 19.

The only explanation for this I can come up with is that it assume that UNII-3 is entirely discarded since it overlaps with the ISM band 5.275-5.825. If this is the case then I believe the question is poorly worded. Just because another band (which many texts plainly state is rarely if ever used) overlaps with another band, does not mean the channels themselves overlap.

Is there another explanation for this? Did I miss something?

Disregard, I believe I know the answer now, the question places the upper boundary of the range as 5.725, likely meaning that the upper UNII band is excluded, leaving 19 channels

Sometimes its not enough to know your material, you have to read the question with a fine toothed comb.

Oi Vey.

Kory, I'm glad you used that phrase: "you have to read the question with a fine toothed comb."

Good certifications require focus on the details in order to test the knowledge of the candidate. For example, the question could have been written simply as:

How many non-overlapping channels are available in the 2.4 GHz ISM band and the UNII range from 5.15 to 5.725?

However, such a simple question would not force you to think as you would have to in the real world, where you are given a scenario and then asked to answer questions about that scenario. The scenarios in the CWNP exams do not tend to be as lengthy as some other vendors, but they are designed to verify practical knowledge rather than just the memorization of facts.

I hope this helps. And good luck on your certification journey.

Frames Are Food,
Tom

thanks for the well wishes, I must say that having sat for 3 different exams in the last 6 months this one has absolutely psyched me out the worst. Its because of questions like this, I am confident that I know the material, but I am not confident in my ability to slow down and carefully read the question for the "gotchas"