The correct answer is that calculated columns consume memory because they are stored as part of the model. This happens because calculated columns in Power BI are defined using Data Analysis Expressions (DAX), a formula language that evaluates row by row during data refresh, not at query time, and the resulting values are physically written into the VertiPaq storage engine. On the Microsoft Power BI Data Analyst PL-300 exam, this concept tests your understanding of the fundamental difference between calculated columns and measures: calculated columns increase model size and memory usage, while measures compute on the fly. A common trap is confusing calculated columns with measures, thinking both are dynamic, but remember that columns are stored and static, whereas measures are volatile and calculated at query time. For exam day, keep this memory tip handy: “Columns cost storage, measures cost CPU.”
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.
Which TWO of the following are true about calculated columns in Power BI?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Calculated columns are computed using DAX formulas.
Option C is correct because calculated columns in Power BI are defined using Data Analysis Expressions (DAX), a formula language specifically designed for data modeling and analysis. These DAX formulas are evaluated row by row during the data refresh process, not at query time, and the results are physically stored in the model.
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.
✗
Calculated columns cannot be used in relationships.
Why it's wrong here
They can be used in relationships.
✗
Calculated columns are evaluated at query time.
Why it's wrong here
They are computed during data refresh.
✓
Calculated columns are computed using DAX formulas.
Why this is correct
DAX is used for calculated columns.
Related concept
Read the scenario before looking for a memorised answer.
✓
Calculated columns consume memory because they are stored as part of the model.
Why this is correct
They are stored in the in-memory column store.
Related concept
Read the scenario before looking for a memorised answer.
✗
Calculated columns are stored on disk and loaded on demand.
Why it's wrong here
They are loaded into memory during refresh.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse calculated columns with measures, mistakenly thinking calculated columns are evaluated at query time (Option B) or that they are not stored in memory (Option E), when in fact calculated columns are materialized during refresh and consume RAM.
Detailed technical explanation
How to think about this question
Under the hood, Power BI uses the VertiPaq in-memory storage engine, which compresses and stores calculated columns alongside imported columns. This means every calculated column increases the memory footprint of the model, which can impact performance on large datasets. A real-world scenario: adding a calculated column for a conditional category (e.g., 'High' vs 'Low' based on sales) will consume memory for every row, whereas a measure performing the same logic would compute on the fly without storage cost.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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.
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: Calculated columns are computed using DAX formulas. — Option C is correct because calculated columns in Power BI are defined using Data Analysis Expressions (DAX), a formula language specifically designed for data modeling and analysis. These DAX formulas are evaluated row by row during the data refresh process, not at query time, and the results are physically stored in the model.
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.
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Question Discussion
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