Subnetting VLSM

Hello everyone, my name is Yoshiki and I have a problem with subnetting.
I am taking cisco course and i'm on the routing topic.
I've been given a practice paper with answers but I'm stuck with it.
The scenario is:
I have been given the address /23
The total number of hosts are 408;
I have to figure the subnet address and subnet mask.
I worked out the subnet mask easily but the addressing is concerning me because I have these addresses: (these are answers)

1| - 90 hosts
8| -100 hosts

Could somebody tell me why 1 and 8 are still on 192.100.10 and why the rest change to .11? I think it has to do with the number of hosts

thanks for you help, I'd apprectice any answer and for someone to point me the correct topic to read .
p.s Sorry for the english
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  1. Try looking at it from a binary standpoint. You have 4 octets (32 bits) and the first 23 bits are always the same... and you can't change those. The remaining 9 bits are yours to address at your discretion. So here's what it looks like:

    192 = 11111111
    100 = 11111111
    10 = 1111111(0 or 1 for the remaining bit)
    0 = 00000000

    The reason some of the networks are .10 and some are .11, is because the last bit of the 3rd octet (the 1 bit) can either be a 1 or 0. If it's a 0, it's the .10 network. If it's a 1, it's the .11 network.

    In your scenario, the two .10 networks are using .128 subnet masks, the 0-127 network and the 128-255 network.

    Does this make sense?
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