Answer:
The whole in this problem is 80.
Explanation:
The answer is 80. In this problem, the number 270 is not mentioned. Therefore, 270 would not be correct. The number 20 is mentioned but it is stating the number of students in 7th grade that have April birthdays, so it is only a portion of the 7th graders. The whole is 80 because that represents the whole population of the 7th grade.