Answer:
20 students.
Step-by-step explanation:
The first person said 5 (which is 5 x 1), the second person said 10 ( which is 5 x2)... we see that this is a arithmetic sequence where the first term is 5 and the nth term is 100. We know that 100 = 5 x 20, therefore, the number of students that counted all the way up to 100 was 20 and Bobby was wrong.