What are the most common MO-210 mistakes that cost otherwise-prepared candidates points?
Specific, avoidable habits rather than knowledge gaps: hard-typing a value where a formula was required, forgetting F4 reference locking before filling a formula down, applying a format to one worksheet when a task meant several grouped sheets, skipping the Document Inspector and workbook-properties skills nobody rehearses, and mixing up COUNT, COUNTA, and COUNTBLANK. None of these require more Excel knowledge — they require knowing they exist.
Checked against Microsoft’s own published pages on September 16, 2026.
The numbers
Typing a value where a formula is required
This is the single most expensive mistake on the exam, and it is entirely avoidable. If a task asks for a calculated result — a sum, an average, a count — the check is looking for an actual formula in the cell, not merely a correct-looking number. A hard-typed value that happens to match earns little or no credit, because the grading reads the formula, not just the displayed result.
The fix is a habit, not a skill: before moving to the next task, glance at the formula bar for any cell you were asked to calculate, not just the cell's displayed content.
Forgetting to lock a reference before filling a formula down or across
A relative reference shifts automatically when a formula is copied or filled. When a formula needs to keep pointing at the same cell — a tax rate, a lookup table's top-left corner — forgetting to lock that reference with F4 (cycling to $A$1) produces a formula that is correct in the first cell and silently wrong in every cell it was filled into.
This is the classic cause of a formula that 'looks right' on inspection of one cell but fails a check applied across a filled range.
Applying a change to one sheet when the task means several
A task written for multiple worksheets — matching a header format, applying the same page setup — requires grouping the relevant sheet tabs (Ctrl-click or Shift-click on the tab bar) before making the change. Skip that step and the edit applies only to whichever sheet is currently active, and every other sheet in scope is left untouched.
There is no visual warning that sheets are ungrouped; the only way to catch this is checking the tab bar before applying the change, not after.
Never having opened the Document Inspector or workbook properties
Both live under File > Info, and most daily Excel users have never deliberately opened either — they sit in the heaviest-weighted domain on the exam precisely because they are not part of routine daily use. A task built around inspecting a workbook for issues, or filling in a built-in property like Title or Author, is checking for exactly those features.
A five-minute rehearsal of both before exam day closes a gap that years of ordinary Excel use does not.
Mixing up COUNT, COUNTA, and COUNTBLANK
COUNT() counts only cells containing numbers. COUNTA() counts any non-empty cell, numeric or text. COUNTBLANK() counts empty cells. The three produce different, all-plausible-looking numbers on the same range, and choosing the wrong one is a silent, easy-to-miss error rather than an obvious one.
What costs people points
Opening a settings dialog, selecting the right option, and closing it without confirming leaves the workbook unchanged. The grader reads the state of the file, not the fact that you knew the right answer — always check the sheet reflects the change before moving on.
Because partial credit is awarded per check within a task, an unattempted task is the only kind that reliably scores zero. Perfecting one difficult task while leaving others completely untouched is a worse outcome than a first pass across everything.
For a practice exam graded on an uploaded file, unsaved changes are invisible to the grader entirely. Save before you upload — this sounds obvious and is nonetheless a real, recurring cause of an unexpectedly low score.
Related questions
What is the single most expensive mistake on MO-210?
Hard-typing a value where the task requires an actual formula. It looks correct on screen and often earns little or no credit, because the grading checks the formula itself, not just the displayed number.
How do I avoid the grouped-worksheet mistake?
Check the tab bar before applying a change meant for multiple sheets — grouped tabs are highlighted, and if the task covers several worksheets, select them all (Ctrl-click or Shift-click) first. Excel gives no separate warning if you forget.
Why do COUNT, COUNTA, and COUNTBLANK get confused so often?
All three return a plausible-looking number for the same range, and the difference between them (numeric cells only, any non-empty cell, or empty cells) is easy to overlook under time pressure unless you have deliberately distinguished them beforehand.
Sources
Read on September 16, 2026. Where this page says something is not published, that means we looked and did not find it — check for yourself.
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