Who asked: Dana, the head of sales at a kitchenware brand, before the planning meeting.
The question: "Overall we grew this year, but I hear one product line is slipping. Which one, by how much, and in which quarter did it go wrong?"
The data: the Sales tab has revenue by product line, quarter and year for 2025 and 2026, 32 rows. The Summary tab is laid out for your answers.
What done looks like: yearly totals and the change for each line, the line with the worst change, its quarter-by-quarter gap, and the quarter to investigate typed in B14.
This case study strings together skills from the Beginner and Intermediate units: SUMIFS with locked ranges, percent change, MIN, and INDEX with MATCH. Each step builds on the one before, and your Summary tab grows as you go.
Read the brief first. Then work through the steps in order; each one starts where the last one ended. The last step asks for a conclusion, not a formula: read your own numbers and type the answer.