Final answer:
The average monthly payment would be most affected by a significantly lower payment observed by Mark. The median is a more appropriate measure of center in the presence of outliers, as it is not heavily influenced by extreme values. Therefore, the correct option is A.
Step-by-step explanation:
When Mark was looking at his monthly utility payments and noticed that one payment was significantly lower than all the others, the measure of center most affected by his observation would be a.) the average monthly payment. This is because the average, or mean, is sensitive to extreme values or outliers. The median, being the middle value of a data set when ordered, would not be as affected by a single low payment, and the mode, being the most frequently occurring value, would also not change based on one low payment. The highest monthly payment would not be affected by one lower payment.
Given that the data set contains an outlier, the most appropriate measure of center for this data would likely be the median, as it is less influenced by the extreme low value and provides a better central tendency for skewed data. Mean can be heavily influenced by the outlier, potentially misrepresenting the central location of the rest of the data. Mode is less informative about the central tendency unless there is a frequently recurring value.