Classful Address Analysis

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Hello all,
I am studying for ccent (icnd1). in chapter 12 of the cisco cert guide, it is talking about "classful" addresses.
on page 345 (if you have the book) it has a chart which summarizes as follows.

Class A address: use 1oct for network, 3oct for host.
Class B adddress: use 2 oct for network 2 for host
Class C address: use 1 oct for network 1 for host.
so far so good.
It gives examples of determining the network ID and Broadcast Address.
For Net ID
class A X.0.0.0,
Class B X.X.0.0
class C X.X.X.0
Broadcast Address:
A X.255.255.255,
B X.X.255.255
C X.X.X.255

All is good with the world
BUT
in the chapter pretest (do I already know this) the last question is:
Which of the following is network Class A,B, or C network id.
a) 10.1.0.0
b) 192.168.1.0
c) 127.0.0.0
d) 172.20.0.1

Well shoot! I just figured it out. BRAIN FART
so the answer is B because it is class C and the last octet is 0. DUH...

so it turns out, Ali is good with the world after all...
so i thought I'd post this after all the typing.
I don't know how many times I've tried explaining a problem to someone only to realize the solution
just by talking about it.

 

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Thanks for the post op very helpful...