Since there is a total of 24 students, and 21 of them did the homework videos. Then we need to find the percent of students that watched the videos.
So we evaluate the quotient of the number of students that watched the videos divided by the total number of students:
21/24 = 0.875
which comes in decimal form. So now we convert it to percent form (bymultiplying it by 100:
0.875 x 100 = 87.5 %
Then 87.5 % of the students watched their homework videos.