Compare the fractions 9/25 and 9/24. To four decimal places, 9/25 = 0.3600 and 9/24 = 0.3750. To four decimal places, these numbers are not equivalent.
In a small group: Picking one person and not putting them back changes the math for the next person significantly.
In a big group: Picking one person and not putting them back doesn't really change anything.
Convenience sampling i
consecutive sampling" (a type of convenience sampling) where they take every patient who enters a specific clinic with a certain condition over a month. While not perfectly random, it is often the only ethical and practical way to gather data in a medical setting.
a systematic sample,
Apply the System:Person 1: 12Person 2: $12 + 50 = \mathbf{62}$Person 3: $62 + 50 = \mathbf{112}$...and so on until you hit 400 names.
parameter
The Solution: You calculate the Statistic (the average of your 100 students) and use it as a "best guess" for the Parameter.