Here is the poor mans method

192.168.100.32 given a subnet mask of 255.255.255.224

Your subnet mask is 255.255.255.224

Take the 224 and subtract it from 256

256 -224 = 32 This tell you your subnet is on a 32 boundary

1st subnet is 0

2nd sub net is 32 this is your subnet

3rd subnet is 64, thus your broadcast addr is 63

To take this a step further.

Lets say you are given a host addr of 192.168.100.112 255.255.255.224

What is the subnet of this host?

We know that the subnet is still on a 32 boundary (subnet mask is still 224)

Now take the host ip and divide it by 32

112 / 32 = 3.5

The third subnet is 64 thus this host subnet is 192.168.100.64 255.255.255.224

Hope this helps

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