AI at work · course 30 of 105

Double-Check AI Spreadsheet Formulas

Check a spreadsheet formula an AI hands you before you paste it in: what the core functions really do, whether it gives the right answer, and which fix does.

3 modules

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What it teaches

How to check a formula an AI assistant hands you before you trust it: what COUNT, COUNTA, AVERAGE, SUMIF, SUMIFS, COUNTIF, VLOOKUP and XLOOKUP actually do (from Microsoft’s own pages), then whether a made-up “AI-written” formula gives the right answer on a small sales sheet, and which fix does: argument order, COUNT vs COUNTA, blanks in averages, unquoted criteria, wildcards, approximate lookups, missing if_not_found, and references that slide when filled down. The AI asks 3 questions, places you, shows a short card and the sheet per module, then gives you one item at a time.

How long

28 items. About 25-40 rounds plus a 12-item final: 1-2 sessions (estimate, not timed with a real student). The tutor gives a one-line save code at the end of each session.

The modules

3 modules, drilled one item at a time.

M0
What the functions actually do
What COUNT, COUNTA, AVERAGE, SUMIF, SUMIFS, COUNTIF, VLOOKUP and XLOOKUP actually do
M1
Is the AI’s formula right?
Is the AI’s formula right for this sheet? Yes or No, and why
M2
Pick the fix
Pick the formula that fixes it (four options)

Before it teaches, it asks

1
What do you use spreadsheets for, and do you ask an AI (ChatGPT, Copilot, Gemini, Claude) to write formulas for you?
2
Task: the total Revenue for the East region. The AI wrote =SUMIF(G2:G13,”East”,C2:C13) in an empty cell. Does it give the right answer here? Say why.
3
Task: in H2, this order’s share of total Revenue, then filled down to H13. The AI wrote =G2/SUM(G2:G13) in H2, then filled down to H13, which gives H13 = 1.0000 here. Which formula gets it right?
A) =$G$2/SUM($G$2:$G$13)
B) =SUM($G$2:$G$13)/G2
C) =G2/SUM($G$2:$G$13)
D) =G2/SUM(G2:G13)

What’s exact, and what isn’t

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Straight from the course’s own notes.

Run, not guessed: Every task’s answer is worked out twice, in plain Python and by running every formula in a spreadsheet formula engine on the same sheet; the script fails if they disagree, or if any option but the key gives the right answer. Two verdicts (an unquoted criterion, VLOOKUP’s default match on an unsorted list) rest on Microsoft’s quoted rule instead, because no engine value settles them.
Quoted: Every rule quotes Microsoft Support’s Excel pages; 14 quotes matched on the live pages 2026-10-11.
Made up for practice: The sheet, the tasks and the “AI-written” formulas. The course makes no claim about how often any AI writes these mistakes.
Not checked in real Excel or Google Sheets: This build machine has neither.
Honest limits: One small sheet; Excel’s functions as Microsoft documents them (Google Sheets mostly matches, but the course doesn’t claim it).
Not in it yet: Asking the AI better questions, pivot tables, dates and text functions, IF and nested logic, dynamic arrays, Google Sheets-only functions.