Simple statistics: counting compound things

While countif() can count the number of times a specific thing appears in a set of cells, countifs() counts the number of times a corresponding set of things appears in a corresponding set of locations.

For example, countif() could count the number of times a certain person taught a class, and it could count the number of times a certain type of class was taught, but it couldn’t count the number of times a certain person taught a certain type of class. However, countifs() can.
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