An organization has a class C network and wants to form a subnet for four departments with hosts as follows:
A:72
B:35
C:20
D:18
what is the possible arrangements?
options:
a) for A: 255.255.255.128 for B: 255.255.255.192 for C & D: 255.255.255.223
b)for A 255.255.255.223 for B: 255.255.255.223 for C & D : 255.255.255.128
My approach for solution:
I just eliminated the rest options and i did it as follows,
for option a) 128=10000000 , so there is $2^{7} = 128$ hosts possible, so it can be for A , again 192= 1100000 so there are $2^{6} = 64 hosts possible , but in 223 = 10110111 means only 4 hosts are possible.
so option A is not possible. But answer given is option A.
I know i am lacking some concept here , please care to correct :)