Hello there! 70% is your answer.
Since the question wants the the probabilities that the student has at least one, but not greater than 2 siblings, add the students that have 1 sibling and have two siblings, 10 + 18 = 28.
Since it can only be 28 students out of the total, put 28 over the total. 28/40, to convert into a percent, divide 28 by 40 and multiply by 100.
28 divided by 40 = 0.7
0.7 multiplied by 100 = 70%
So, the experimental probability that a student has at least one, but not greater than 2 siblings is 28/40 or 70%. I hope this was helpful and have a great rest of your day! :)