Ten questions a help desk manager might ask, all on the Northwind Help Desk data. Each needs a calculated field. Some need an aggregate calculation (a ratio of totals), some a row level one, and a few depend on handling NULLs correctly.
Before you write a calculation, decide its level. Does the answer belong to each ticket (row level), or to a group of tickets (aggregate, with SUM, COUNT or AVG inside)? If you mix the two, Tableau tells you it can't mix aggregate and non-aggregate arguments.
Name each field as the task says.