Practice exercises

Fetching a value from another column by matching a key — the single most-used skill in any real spreadsheet.

When a key repeats, the default lookup gives you the oldest row — usually the opposite of what you want.

The first formula everybody learns, and the one place a typed-out chain of plus signs still costs people an afternoon.

Aggregating a slice of the data instead of all of it — the step from a total to a report.

COUNTIFS with two criteria — where "how many" questions actually start.

Top-n answers that do not disturb the sheet — and do not break when two values tie.

Extracting part of a text value — the task behind most spreadsheet cleanup work.

Date arithmetic that respects weekends — the difference between a calendar and a delivery promise.

Adding 30 days looks right until it lands on the 2nd of the wrong month. This is the trap behind every subscription date.

Four thresholds, one readable formula. The nested-IF version is where bracket-counting errors come from.

A column of #N/A is not a bug — but shipping it to a reader is. Handling the expected failure without hiding the real ones.

Two values that look identical and refuse to match. This is the most-reported and least-understood spreadsheet bug there is.