Final answer:
The question is about determining missing frequencies in a data set where the median is given, but it cannot be accurately answered without additional data about the distribution.
Step-by-step explanation:
The student is asking how to find the missing frequencies x and y for a data set where the median is 20.75, and the total frequency is 100. To solve this problem, one must understand how to use the concept of the median in a frequency distribution, as well as applying the constraints that the total frequency should add up to 100.
However, based on the provided information, it's not possible to derive a clear method or solve for the exact frequencies x and y without additional data such as the interval in which the median lies or the other frequencies in the distribution.
The typical process involves arranging data in ascending order, finding the cumulative frequencies, and then determining the median by identifying the value that lies in the middle of the data set considering their frequencies.