The correct DAX expression is DATEDIFF(Orders[OrderDate], Orders[ShipDate], DAY). This works because the DATEDIFF function calculates the interval between two dates in the specified unit—here, DAY—making it the precise tool for computing the days between OrderDate and ShipDate in a calculated column. On the Microsoft Power BI Data Analyst PL-300 exam, this question tests your ability to apply date-time functions in DAX, a core skill for data modeling and reporting. A common trap is confusing DATEDIFF with DATEDIFF in SQL or using the wrong unit argument, such as HOUR or MONTH, which would yield incorrect results. Remember that DATEDIFF always requires three arguments: the start date, the end date, and the interval unit. For days between two dates, always specify DAY as the third argument, and note that the function counts full intervals, so the result is an integer representing the number of day boundaries crossed. A helpful memory tip: “DATEDIFF needs a start, an end, and a unit—DAY for days between.”
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 table named Orders that contains columns OrderDate, ShipDate, and CustomerID. You need to create a calculated column that computes the number of days between OrderDate and ShipDate. Which DAX expression should you use?
Option A is correct because the DATEDIFF function in DAX calculates the interval between two dates in the specified unit (DAY). This directly computes the number of days between OrderDate and ShipDate, which is the required result for the calculated column.
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.
DATEDIFF returns the number of intervals between two dates; DAY specifies the interval.
Related concept
Read the scenario before looking for a memorised answer.
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DATEADD(Orders[OrderDate], 1, DAY)
Why it's wrong here
DATEADD adds a specified number of intervals to a date, not compute difference between two dates.
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DAY(Orders[ShipDate] - Orders[OrderDate])
Why it's wrong here
DAY returns the day of the month, not the difference in days.
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NETWORKDAYS(Orders[OrderDate], Orders[ShipDate])
Why it's wrong here
NETWORKDAYS is not a standard DAX function; it may be a custom function or from another tool.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates might confuse DATEDIFF with DATEADD (which shifts dates) or incorrectly use DAY() on a date difference, thinking it extracts the number of days, when DAY() actually returns the day of the month (1–31).
Detailed technical explanation
How to think about this question
DATEDIFF returns an integer representing the count of datepart boundaries crossed between two dates, which is ideal for calculating elapsed days. In DAX, date arithmetic (e.g., Orders[ShipDate] - Orders[OrderDate]) returns a decimal representing the number of days and fractional time, but this can be unreliable for precise day counts due to time components. A real-world scenario is calculating shipping lead times for logistics analysis, where DATEDIFF ensures consistent integer results regardless of time values in the date columns.
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: DATEDIFF(Orders[OrderDate], Orders[ShipDate], DAY) — Option A is correct because the DATEDIFF function in DAX calculates the interval between two dates in the specified unit (DAY). This directly computes the number of days between OrderDate and ShipDate, which is the required result for the calculated column.
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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