CompTIA Network+ N10-006 Q27

Corporate headquarters provided your office a portion of their class B subnet to use at a new office location. Allocate the minimum number of addresses (using CIDR notation) needed to accommodate each department.
q27a
After accommodating each department, identify the unused portion of the subnet by responding to the question on the graphic. All drop downs must be filled.
Instructions: When the simulation is complete, please select the Done button to submit.
All Networks have the range from /0 to/32
Hot Area:
q27b-hot-area

q27-answer

Section: Network architecture

Explanation:
An IPv4 address consists of 32 bits. The first x number of bits in the address is the network address and the remaining bits are used for the host addresses. The subnet mask defines how many bits form the network address and from that, we can calculate how many bits are used for the host addresses.
The formula to calculate the number of hosts in a subnet is 2n – 2. The “n” in the host’s formula represents the number of bits used for host addressing. If we apply the formula (22 – 2), we can determine that the following subnets should be configured:
Sales network – /26 – This will provide up to 62 usable IP addresses (64-2 for subnet and broadcast IP)
HR network – /27 – This will provide for up to 30 usable IP’s (32-2)
IT – /28 – This will provide for up to 14 usable IP’s (16-2)
Finance – /26 – Note that a /27 is 32 IP addresses but 2 of those are reserved for the network and broadcast IP’s and can’t be used for hosts.
Marketing – /28
If we add up how many IP blocks are used that is 64+32+16+64+16=192.
A /24 contains 256 IP addresses, so 256-192=64.
So the last unused box should be a /26, which equates to 64 addresses