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Choose a topic, a skill or a difficulty. Calculation exercises have new versions with fresh numbers once you have solved them, so you can practise the method rather than memorise an answer.

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Interpretation, difficulty 3 of 3

Customers or transactions?

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An online retailer exports a table with one row per transaction: customer ID, date, basket value. An analyst counts 12,400 rows, reports “12,400 customers” and computes the mean basket value as “the average customer's spend”. In two or three sentences, explain the problem and how to fix it.