The answer is to create a separate category indicating missingness and impute with a placeholder. This is the most robust strategy for handling MNAR missing data because when the missingness is related to the age value itself, the fact that a value is absent carries meaningful information about the underlying distribution. Simply imputing with the mean or median would ignore this systematic difference, biasing the model by treating missing values as if they were randomly distributed. On the AWS Certified Machine Learning Specialty exam, this question tests your understanding of missing data mechanisms—specifically that MNAR requires a structural approach rather than a statistical one. A common trap is to default to mean or median imputation, which works for MCAR or MAR but fails here. Remember the mnemonic: "MNAR means the missingness matters—flag it, don't fill it."
MLS-C01 Exploratory Data Analysis Practice Question
This MLS-C01 practice question tests your understanding of exploratory data analysis. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
During EDA, a data scientist finds that a feature 'age' has 30% missing values. The dataset has 100,000 rows. Which imputation strategy is most robust if the data is not missing at random (MNAR) and the missingness is related to the age value itself?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a separate category indicating missingness and impute with a placeholder
Option C is correct because missingness related to the value itself means that the missing data are systematically different; creating a 'missing' category allows the model to learn the pattern. Option A is wrong because mean imputation reduces variance and ignores the systematic difference. Option B is wrong because median imputation has similar issues. Option D is wrong because random imputation introduces noise without capturing the missingness pattern.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Impute with the mean age
Why it's wrong here
Mean imputation assumes data is missing completely at random (MCAR), not MNAR.
✗
Impute with a random sample from the observed ages
Why it's wrong here
Random imputation assumes MCAR and adds noise.
✗
Impute with the median age
Why it's wrong here
Median imputation also assumes MCAR.
✓
Create a separate category indicating missingness and impute with a placeholder
Why this is correct
Creating a missing category captures the information that the value is missing, which is informative under MNAR.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related MLS-C01 NAT questions on configuration and troubleshooting.
Exploratory Data Analysis — This question tests Exploratory Data Analysis — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Create a separate category indicating missingness and impute with a placeholder — Option C is correct because missingness related to the value itself means that the missing data are systematically different; creating a 'missing' category allows the model to learn the pattern. Option A is wrong because mean imputation reduces variance and ignores the systematic difference. Option B is wrong because median imputation has similar issues. Option D is wrong because random imputation introduces noise without capturing the missingness pattern.
What should I do if I get this MLS-C01 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related MLS-C01 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This MLS-C01 practice question is part of Courseiva's free Amazon Web Services 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 MLS-C01 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.