To find the median, you first need to arrange the data in ascending order.
The provided data is: 30, 35, 28, 40, 25.
Arranging these numbers in ascending order gives us: 25, 28, 30, 35, 40.
Since there are 5 numbers, the median is the middle number. The middle number in this ordered list is the 3rd number.
Therefore, the median number of units sold is 30.