What is the most efficient subnet for 31 laptops?
Short answer
C 10.10.10.0/26
Question
Key Takeaways
This question tests your ability to identify the most efficient subnet by comparing usable host counts, with the common trap being to confuse total IPs in the subnet with usable IPs after subtracting network and broadcast addresses.
On the CompTIA Network+ N10-008 exam, finding the smallest subnet that supports 31 usable hosts requires knowing the formula 2^(32-prefix) - 2. The community consensus is that 10.10.10.0/26 is correct because it provides 62 usable addresses, while /27 only provides 30.
Common mistake: The most common wrong answer is D (10.10.10.0/27) because it has 32 total IPs, which seems enough for 31 laptops, but only 30 are usable after reserving the network and broadcast addresses.
Expert Analysis
Why the Answer Is Correct
Option C (10.10.10.0/26) is correct. A /26 subnet has 2^(32-26) = 64 total addresses, of which 2 are reserved for the network and broadcast addresses, giving 62 usable host addresses. This is the smallest prefix that supports 31 laptops while leaving room for growth.
Why the Other Options Are Wrong
Option A (/24) and Option B (/25) provide 254 and 126 usable addresses respectively, which are larger than necessary and less efficient. Option D (/27) has only 32 total addresses, minus 2 reserved, leaving just 30 usable addresses, which is not enough for 31 laptops.
Community Comment Notes
Several commenters correctly explain the math. Comment 1 notes that /27 gives 30 usable and concludes /26 is needed. Comment 2 highlights that /26 gives 64 minus 2 for broadcast and network ID equals 62. Comment 3 directly compares the host requirements and confirms /27 is too small. The strong vote count for C (94) reflects clear consensus.
Official Reference
https://www.comptia.org/certifications/network
This link opens the official vendor documentation in a new tab.
Exam Strategy
Memorize the usable host formula: 2^(32-prefix) - 2. On the exam, when asked for the 'most efficient' subnet, start with the smallest prefix that might work, calculate its usable hosts, and if it is insufficient, move to the next larger prefix. In this case, /27 gives 30 usable, so the answer must be /26.
Community Votes
100% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 6 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 6
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Roman_Kwo 👍 9 Answered CShould be 10.10.10.0/26 (64IPs - 2 = 62 usable) 10.10.10.0/27 is 32 IPs - 2 = 30 usable. We need to fit 31 IPs therefore it should be /26. Correct me if I am wrong.
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kinny4000 👍 4We need 31 hosts. /27 = 32 hosts BUT 2 are reserved for network and broadcast addresses (30 hosts) . /26 is the right answer (62 hosts)
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jagoichi 👍 4 Answered C/26 gives us 64 minus 2 for BR and Net ID 62 /27 is to few 32 minus 2 = 30
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Marinos_89 👍 1 Answered B32bit - /26= 7 2^7= 64 64-2=62 ips
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BigDazza_111 👍 4 Answered CC is correct, easy
Show 1 more comment
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aed0e20 👍 4C is the answer
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