Subnetting doubt

[sai]

Which three ip address can be assign to hosts if the subnet mask is /27 and subnet zero is usable(choose 3)

1. 10.15.32.17
2. 17.15.66.128
3. 66.55.128.1
4. 135.1.64.34
5. 129.32.192.192
6. 192.168.5.63

plz help me to understand to do the answer.

[Fuzz]

Take each address and apply the /27 mask to it. Now work out if the address is a valid host address in this subnet.

For instance, 17.15.66.128 /27. What's the block size? 32 right? So where are our subnets? .32, .64, .96 and .128 which is our address, so this cannot be a host address, it is a subnet address.

Eventually you will be able to see the answer without having to work it out. I can immediately see 3 host addresses, 2 subnet addresses and one broadcast address from those listed with that mask.

[sai]

thank u sir..! as its /27, we must be concerned only about 4th octet....right??

[Fuzz]

Correct, all other octets will stay the same.

[sai]

ya..got it.. thx sir :)