It is said in the question that one is randomly selected, but there is no specified number of times. So you can draw ten times to decide 10 students to participate in the activity.

And your rules, statistically speaking, have different probabilities, which means unfairness.

50 people, and the probability that one of them can go is 1/50. According to your thinking, if you draw the 25th, you should go to 25th-16th.

But for the 24th, if you draw any of the 24th-33rd, he can go. What are the chances that he will go on the 24th? 1/5.

Do you think there is a one-in-five chance for 50 people to go on the 24th? Do you think it's appropriate?