To determine how many cells are in anaphase, you'd need to observe a population of dividing cells under a microscope and accurately stage them based on their appearance. During mitosis, anaphase is characterized by the separation of sister chromatids, which begin to move toward opposite poles of the cell.
In a typical population of cells undergoing mitosis, the number of cells in anaphase can vary depending on the specific conditions, timing, and duration of the observation. For example, in a well-staged sample, you might find that 10-20% of the cells are in anaphase at any given moment, depending on the length of the cell cycle and any synchronization treatments that may have been applied.
If you are working on a specific experiment or observation, it's essential to count the cells directly under the microscope to get an accurate number.