- A
255.255.255.128 (/25)
Why wrong: /25 provides 126 usable hosts, which is more than needed and wastes addresses.
- B
255.255.255.192 (/26)
/26 provides 62 usable hosts, which is the smallest subnet that can accommodate 50 devices.
- C
255.255.255.224 (/27)
Why wrong: /27 only provides 30 usable hosts, which is too few.
- D
255.255.255.240 (/28)
Why wrong: /28 only provides 14 usable hosts, far too few.
Question 31 of 520
N10-009 Networking Concepts Practice Question
This N10-009 practice question tests your understanding of networking concepts. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company needs a subnet that will support exactly 50 devices. Which subnet mask provides the minimum number of usable host addresses while still accommodating the requirement?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
255.255.255.192 (/26)
Option B (255.255.255.192, /26) provides 2^(32-26) - 2 = 62 usable host addresses, which is the smallest subnet that supports exactly 50 devices. A /27 yields only 30 usable addresses (too few), while a /25 yields 126 usable addresses (wasteful). The requirement is to minimize waste while meeting the need.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
255.255.255.128 (/25)
Why it's wrong here
/25 provides 126 usable hosts, which is more than needed and wastes addresses.
When this WOULD be correct
A company needs a subnet that supports exactly 100 devices. The /25 subnet provides 126 usable addresses, which is the minimum that can accommodate 100 hosts.
- ✓
255.255.255.192 (/26)
Why this is correct
/26 provides 62 usable hosts, which is the smallest subnet that can accommodate 50 devices.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
255.255.255.224 (/27)
Why it's wrong here
/27 only provides 30 usable hosts, which is too few.
When this WOULD be correct
This subnet mask would be correct if the requirement were to support exactly 30 devices, or if the question asked for the subnet mask that wastes the fewest addresses while supporting up to 30 hosts.
- ✗
255.255.255.240 (/28)
Why it's wrong here
/28 only provides 14 usable hosts, far too few.
When this WOULD be correct
This subnet mask would be correct for a network requiring exactly 14 usable host addresses, such as a small branch office with 10-12 devices and a few reserved addresses.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓255.255.255.192 (/26)Correct answer▾
Why this is correct
/26 provides 62 usable hosts, which is the smallest subnet that can accommodate 50 devices.
✗255.255.255.128 (/25)Wrong answer — click to see why▾
Why this is wrong here
A /25 subnet provides 126 usable host addresses, which exceeds the requirement of 50 devices and is not the minimum.
★ When this WOULD be the correct answer
A company needs a subnet that supports exactly 100 devices. The /25 subnet provides 126 usable addresses, which is the minimum that can accommodate 100 hosts.
Why candidates choose this
Candidates may mistakenly think that a /25 is the smallest subnet that can support 50 devices, not realizing that /26 (62 usable addresses) is sufficient and more efficient.
✗255.255.255.224 (/27)Wrong answer — click to see why▾
Why this is wrong here
A /27 subnet provides only 30 usable host addresses (2^5 - 2 = 30), which is insufficient for 50 devices.
★ When this WOULD be the correct answer
This subnet mask would be correct if the requirement were to support exactly 30 devices, or if the question asked for the subnet mask that wastes the fewest addresses while supporting up to 30 hosts.
Why candidates choose this
Candidates may mistakenly think 2^5 = 32 is enough for 50 devices, or they confuse the number of addresses (32) with usable hosts (30) and overlook the need for 50.
✗255.255.255.240 (/28)Wrong answer — click to see why▾
Why this is wrong here
A /28 subnet provides only 14 usable host addresses (2^(32-28)-2 = 14), which is insufficient for 50 devices.
★ When this WOULD be the correct answer
This subnet mask would be correct for a network requiring exactly 14 usable host addresses, such as a small branch office with 10-12 devices and a few reserved addresses.
Why candidates choose this
Candidates may mistakenly think that a /28 (240) is sufficient because they forget to subtract the network and broadcast addresses, or they misapply the formula for usable hosts.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The N10-009 exam often tests the candidate's ability to distinguish between total addresses and usable host addresses, with the trap being that candidates forget to subtract the network and broadcast addresses, leading them to incorrectly select a /27 (which has 32 total addresses but only 30 usable).
Detailed technical explanation
How to think about this question
The usable host count is derived from the formula 2^(32 - prefix_length) - 2, where the two subtracted addresses are the network address (all host bits 0) and the broadcast address (all host bits 1). In IPv4 subnetting, the /26 mask (255.255.255.192) borrows 2 bits from the host portion of a /24, creating 4 subnets each with 62 usable addresses. Real-world scenarios like VLAN sizing or point-to-point links require precise subnet selection to avoid IP exhaustion or waste.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Visual reference
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this N10-009 question test?
Networking Concepts — This question tests Networking Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 255.255.255.192 (/26) — Option B (255.255.255.192, /26) provides 2^(32-26) - 2 = 62 usable host addresses, which is the smallest subnet that supports exactly 50 devices. A /27 yields only 30 usable addresses (too few), while a /25 yields 126 usable addresses (wasteful). The requirement is to minimize waste while meeting the need.
What should I do if I get this N10-009 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 11, 2026
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.
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