A shopkeeper records 12, 4, 7, 20 and 9 sales on five days. What is the median number of sales?

Explicación

Ordering the five daily totals gives 4, 7, 9, 12 and 20, and the central one of the five positions holds 9, so the median is 9 sales. Answering 7 sales takes the entry standing in the middle of the unordered record, which sits there only because of the sequence in which the days were written down.