Understanding Network+ Exam answer

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Hi all

Taking some practice exams as part of my Network+ studies and I've come up against a question where I don't understand why the answer is what it is. Is the key word "BEST" and if so, again why is /16 the answer?

Sorry if it's a daft question

Hey @Graham-Jenkins great question, here is what I see about this question/answer:

Based on the networks 10.8.16.0/22 and 10.8.31.0/21, which of the following is the BEST summarized CIDR notation?

A. 10.8.0.0/16 <<The practice exam says this is right (I believe this is wrong)
B. 10.8.0.0/19 << I believe this should be the correct answer
C. 10.8.0.0/20
D. 10.0.0.0/24

the following is true:

00001010 00001000 00010000 00000000 10.8.16.0/22   
00001010 00001000 00011111 00000000 10.8.31.0/21
------------------------------------------------
11111111 11111111 11100000 00000000 or /19 

Unless the question was asking for a summarization to the network boundary, then:

00001010 00001000 00010000 00000000 10.8.16.0/22
00001010 00001000 00011111 00000000 10.8.31.0/21
------------------------------------------------
11111111 11111111 00000000 00000000 or /16 summarizes the BEST

Base on the context though, /19 is the best choice. I hope this helps!

To add to @wes-bryan excellent answer here.

If the question were to read " summarize to network boundary," then the offered answer of A would be correct. But given, the math shown by Wes, I would concur with both of you.