The answer is to rewrite the measure using CALCULATE with a simple SUM instead of SUMX. This improves performance because SUMX is an iterator that evaluates an expression row by row over a table, which is computationally expensive, whereas a base measure using SUM is a storage-engine-friendly aggregation that can be pre-calculated and cached. By wrapping that base measure in CALCULATE, you apply the necessary filter context without forcing the engine to scan every row, drastically reducing query time while preserving the same business logic. On the PL-300 exam, this question tests your understanding of the difference between iterator functions and aggregator functions, and it often appears as a trap where candidates mistakenly choose to remove filters or add KEEPFILTERS. A common memory tip is: “Iterate only when you must; aggregate and calculate for speed.”
PL-300 Model the data Practice Question
This PL-300 practice question tests your understanding of model 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 have a Power BI model with a measure that calculates total sales using SUMX over a filtered table. The measure performs slowly. Which change will most likely improve performance without altering business logic?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Rewrite the measure using CALCULATE with a simple SUM instead of SUMX
Option B is correct: Using a base measure for SUM of Sales Amount and then applying filter context often performs better than iterating with SUMX. Option A is wrong because removing filters may change logic. Option C is wrong because increasing storage mode changes data source behavior but may not be allowed. Option D is wrong because KEEPFILTERS can add overhead.
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.
✗
Add KEEPFILTERS to preserve existing filters
Why it's wrong here
Does not address performance; may add overhead.
✓
Rewrite the measure using CALCULATE with a simple SUM instead of SUMX
Why this is correct
CALCULATE is more efficient than iterating over rows.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Change the storage mode of the table from Import to DirectQuery
Why it's wrong here
May not improve performance and could degrade it.
✗
Remove all filter functions from the measure
Why it's wrong here
Would change the logic of the measure.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which PL-300 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Model the data — This question tests Model the data — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Rewrite the measure using CALCULATE with a simple SUM instead of SUMX — Option B is correct: Using a base measure for SUM of Sales Amount and then applying filter context often performs better than iterating with SUMX. Option A is wrong because removing filters may change logic. Option C is wrong because increasing storage mode changes data source behavior but may not be allowed. Option D is wrong because KEEPFILTERS can add overhead.
What should I do if I get this PL-300 question wrong?
Identify which PL-300 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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