Comfort with a basic spreadsheet or calculator. Coding is optional.
A spreadsheet or calculator; optional local Python. Text-only AI can explain a plan but cannot establish that calculations ran.
Start with the idea
Define what you are counting before calculating an average.
State what one row represents, the units and which rows belong in the question. Missing is different from zero. Report excluded or unresolved rows separately.
Denominator: The count or quantity you divide by when calculating a rate or average.
See the example and check your understanding
A made-up teaching example
Two closed requests took thirty and forty-five minutes. An open request has no duration. The closed-request mean is 37.5 minutes, using two observations.
Ask yourself
Should the open request enter the completed-duration average as zero?
Show the explanation
No. That changes the total you divide by and the meaning. The result describes only the two closed sample requests.
Start with these checks
- Define the row unit and question.
- Separate open and invalid records.
- Keep missing values different from zero.
Use the different practice case below and check every requirement in its full instructions.
Full learning objectives
- Identify row meaning, units and scope.
- Set missing-value and exclusion rules.
- Distinguish a calculation plan from executed work.
Captions appear here during playback.
Define the question and the data contract
Define what you are counting before calculating an average.
Video playback is unavailable. Read the descriptive transcript below, go directly to practice, or open the video file.
Source-based teaching example · Fictional data · Reviewed 2026-10-03. Microsoft Mark · locally synthesized. On a small screen, use fullscreen for diagram details or read the transcript.
Read the descriptive transcript
0:00 · What you will learn
Define what you are counting before calculating an average.
What appears on screen
Define what you are counting before calculating an average.
0:06 · The idea
State what one row represents, the units and which rows belong in the question. Missing is different from zero. Report excluded or unresolved rows separately.
What appears on screen
State what one row represents, the units and which rows belong in the question. Missing is different from zero. Report excluded or unresolved rows separately.
0:19 · One useful term
Denominator. The count or quantity you divide by when calculating a rate or average.
What appears on screen
The count or quantity you divide by when calculating a rate or average.
0:28 · A worked example
Two closed requests took thirty and forty-five minutes. An open request has no duration. The closed-request mean is 37.5 minutes, using two observations.
What appears on screen
Two closed requests took thirty and forty-five minutes. An open request has no duration. The closed-request mean is 37.5 minutes, using two observations.
0:43 · Your turn to think
Should the open request enter the completed-duration average as zero? Pause and decide before continuing.
What appears on screen
Should the open request enter the completed-duration average as zero? Pause the video if you need more time.
1:01 · Why this answer works
No. That changes the total you divide by and the meaning. The result describes only the two closed sample requests.
What appears on screen
No. That changes the total you divide by and the meaning. The result describes only the two closed sample requests.
1:12 · Check 1
Define the row unit and question.
What appears on screen
Define the row unit and question.
1:17 · Check 2
Separate open and invalid records.
What appears on screen
Separate open and invalid records.
1:22 · Check 3
Keep missing values different from zero.
What appears on screen
Keep missing values different from zero.
1:27 · Now try a different case
Open the lesson and try its different practice case. Use every check in the full task. Watching alone does not mark the lesson complete.
What appears on screen
Open the lesson Try the new case Check and revise The full task and its requirements are in the linked lesson.
Watching explains the example. Complete the lesson practice to check what you can do. Explore all visual lessons →
The method
Start with the decision and define what one row represents. A request, a customer and a monthly total are different units. Record field names, units, period, population and provenance. Inspect a sample and count rows before asking for analysis. Never upload personal or organizational records to an unapproved environment; the supplied cases are fictional.
Ask AI to propose formulas and assumptions, then inspect them. A text-only assistant may describe calculations without executing them. A spreadsheet or code tool can execute, but you must inspect its inputs, formulas and output. Missing values are not automatically zero. Specify how duplicates, invalid entries and exclusions are handled before comparing groups.
Choose your model, harness and offline route
Text-only assistant
Use supplied text. Ask for a plan or draft; do not claim browsing, code execution or file access that was unavailable.
Tool-enabled application or harness
Record which tools actually run, allowed files and actions, approval boundaries and observable results. Tools are optional unless the task needs them.
Local or cloud deployment
Inspect inference, retrieval, connectors, logs and storage separately. Use only authorized environments for real data; training fixtures are fictional.
Higher-capability or frontier model
Evaluate the exact task and configuration. Capability does not supply missing evidence or grant permission. No provider ranking or guarantee is implied.
Offline alternative
Use the supplied inputs and inspect the worked example manually. Builder exercises use local deterministic Python. No paid account or live model call is required.
Record the exact product/model label when available, tools actually used, inputs, permitted actions, observed output and checks. Live accounts or APIs may have external costs; they are optional and are not used by this page.
Read the general workflow guide →Worked example
Supplied input
Fictional table: row A = one closed request, duration 30 minutes; B = one closed request, duration 45; C = open request, duration blank. Question: average duration of closed requests in this sample.
A checked result
Contract: one row per request; minutes; closed only; exclude open C from completed-duration mean and report it separately. Mean = (30 + 45) / 2 = 37.5 minutes.
Why this works
Using zero for C changes both the denominator and the meaning. The result describes two closed sample requests only.
Try a different case
Independent rows: X closed 20 minutes; Y closed 40; Z open blank; W closed duration -5. Define a contract and an analysis plan before calculating.
Download this task and checklist →Interactive practice / Fictional fixture
Choose the valid analysis population
Use the supplied independent case above. Check the bounded decisions, then review your written artifact against the full acceptance criteria.
Everything runs in this browser. No AI model is called and no work is uploaded. Bounded checks cover specific facts and rules. Your writing is not graded: you review it yourself. Practice never marks a lesson complete automatically.
Define row meaning, units, closed status, missingness and invalid-record review.
Try the task, run the checks, then revise. Checks are teaching feedback, not an instructor grade.
Observed browser simulation
This trace comes from the bounded local checker. It is not a Python run, model result or production tool execution.
Self-review
Locked. Write every written part, then run the checks. A few words is not an attempt.
This is self-review, not grading. Read our answers, then tick what your own work does. Ticks are optional. They stay on this page and are not saved or sent anywhere. A different answer can be just as good if it meets the lesson criteria.
Your data contract and exclusion note
A strong answer
Row meaning: one row is one case. Unit: minutes from open to close. Population for the mean: cases with status closed and a duration above zero. Z is open with a blank duration: leave it out of the mean and report it as one open case. W is closed with -5: a duration cannot be negative, so flag it as invalid, keep it in the review log and do not correct it. Plan: mean of X and Y. Report it as the mean of two usable closed cases out of three closed, with one invalid record.
A flawed answer
Average all four rows. Treat Z as 0 because it has no time yet, and change W to 5 since the minus sign is clearly a typo. Report the average duration.
What is wrong with it: Zero for an open case invents a duration and drags the mean down. Changing -5 to 5 is a guess recorded as data. The result would also be reported with no word on what was changed.
Keep or restore your work
Drafts are not saved automatically. Save only fictional practice data. A browser draft may be lost if storage is cleared; download a copy to keep it.
Your steps
- State the population, row meaning and unit.
- Flag W as invalid and Z as open, rather than silently deleting them.
- Calculate a valid observed closed-request mean and report exclusions.
Check your work
- Mean of valid observed closed durations is 30 minutes.
- Report one open and one invalid record.
- Do not claim a mean for all requests or treat blanks as zero.
After your attempt: review notes and a common mistake
A 30-minute mean is conditional on the two usable records. The invalid closed record means coverage is incomplete; simply reporting “average 30” without that limit is misleading.
Different wording or a different justified decision can pass. Check your work against every requirement; these notes are not an automated grade.
Explain your approach
What additional data would you need for a complete closed-request average?
Keep your artifact, one correction or decision, its evidence and one remaining limitation. Nothing on this page sends or uploads your work.
Check your understanding
Choose an answer to see feedback. This is a knowledge check, not instructor assessment.
Review your independent practice
Complete the supplied task before recording progress. Use the acceptance criteria and reveal the review notes after your attempt. Keep your artifact yourself; nothing is uploaded.
Not yet self-reviewed. Completion stays in this browser and does not issue a badge.
Optional deeper study
Explore the related general-course lesson → This opens the existing canonical lesson; it is optional depth, not another copy of this focused task.
Primary references
Revision 2026-10-03. Fictional examples, not observed provider results. Knowledge checks and completion records are self-study aids.