Question

In Network Subnetting ....:
To calc the number of hosts per subnet :
2(number of zeros) -2
we subtract 2 because there are 2 addresses we can't use :
The first address which is the subnet number and the last address which is the broadcast address
To calc the numbers of networks per subnet :
2^(number of ones) -2
why do we subtract 2 ?

Answer 1

as I remember the number of subnets is (number of ip addresses)/(number of hosts + 2)

Answer 2

192.168.0.0/24 and 192.168.0.0/16, 192.168.255.255/16 and 192.168.255.255/24 would be ambiguous.