The correct actions are to remove derived columns like TotalCharges and set CustomerID as a unique primary key. TotalCharges is a derived column because it can be calculated as MonthlyCharges multiplied by TenureMonths, so removing it reduces data redundancy, shrinks model size, and prevents update anomalies—a core principle of optimizing a Power BI model for performance. On the PL-300 exam, this tests your understanding of star schema best practices and data quality, where the common trap is keeping calculated columns that bloat the model or failing to designate a proper primary key for relationships. To remember, think “remove the math, mark the ID”—if a column can be derived from others, drop it; then always set a unique identifier as the primary column to ensure row-level integrity and efficient joins.
PL-300 Prepare the data Practice Question
This PL-300 practice question tests your understanding of prepare the data. 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.
You are preparing data for a Power BI report that analyzes customer churn. The source data contains the following columns: CustomerID, Churn (Yes/No), AgeGroup (Teen, Adult, Senior), SubscriptionType (Basic, Premium), MonthlyCharges, TotalCharges, TenureMonths. You need to ensure data quality and optimize the model. Which TWO actions should you take? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove TotalCharges column if it can be calculated from MonthlyCharges and TenureMonths.
Option C is correct because removing derived columns like TotalCharges (which equals MonthlyCharges × TenureMonths) reduces data redundancy, improves model size, and avoids potential inconsistencies. Option D is correct because setting CustomerID as a unique key and marking it as the primary column ensures proper row-level identity, enables efficient relationships, and is a best practice for star schema modeling in Power BI.
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.
✗
Convert Churn column to a numeric 0/1 column.
Why it's wrong here
Churn is best kept as text for filtering; can be aggregated in measures.
✗
Create a calculated column for AverageCharges per customer.
Why it's wrong here
Not necessary for data preparation; can be done in measures.
✓
Remove TotalCharges column if it can be calculated from MonthlyCharges and TenureMonths.
Why this is correct
Reduces model size and redundancy.
Related concept
Read the scenario before looking for a memorised answer.
✓
Set CustomerID as a unique key and mark it as the primary column.
Why this is correct
Ensures relationships work correctly.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create a separate table for subscription types.
Why it's wrong here
Only two types; not necessary to normalize.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Microsoft often tests the distinction between calculated columns and measures, leading candidates to choose Option B (creating a calculated column for an aggregation) instead of recognizing that such aggregations belong in measures to avoid bloating the model and breaking filter context.
Detailed technical explanation
How to think about this question
In Power BI, removing derived columns reduces the VertiPaq storage engine's memory footprint because each column is compressed independently; storing TotalCharges when it is a simple product of two other columns wastes space and can cause refresh anomalies if the source data is inconsistent. Marking CustomerID as the primary key (via 'Mark as Date Table' is not applicable here; instead, ensure no duplicates exist and set the column's 'Is Key' property in Power Query or use the 'Mark as Primary Key' option in model view) enables Power BI to optimize query plans and enforce referential integrity when building relationships. The trap here is that candidates often confuse 'calculated column' with 'measure' — a calculated column is evaluated row-by-row and stored, while a measure is evaluated at query time and respects filters, making it the correct choice for aggregations like average charges per customer.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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.
Prepare the data — This question tests Prepare the data — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Remove TotalCharges column if it can be calculated from MonthlyCharges and TenureMonths. — Option C is correct because removing derived columns like TotalCharges (which equals MonthlyCharges × TenureMonths) reduces data redundancy, improves model size, and avoids potential inconsistencies. Option D is correct because setting CustomerID as a unique key and marking it as the primary column ensures proper row-level identity, enables efficient relationships, and is a best practice for star schema modeling in Power BI.
What should I do if I get this PL-300 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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 PL-300 practice question is part of Courseiva's free Microsoft 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 PL-300 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.