What is the mode of the following set of numbers: 86, 98, 98, 98, 115, 120, 45, 210, 320?

The mode of a set of numbers is defined as the number that appears most frequently within that set. In the given list of numbers—86, 98, 98, 98, 115, 120, 45, 210, 320—the number 98 occurs three times, while all other numbers appear only once. Therefore, since 98 is the number that appears with the highest frequency, it is identified as the mode of the set. This makes it the correct answer. The concept of mode is crucial in statistics, as it helps in understanding the most common value in a data set, which can be important for data analysis and interpretation in various fields, including nursing and healthcare statistics.