To ensure that every student receives one donut, you need to purchase enough dozens of donuts to cover 284 students. To find out how many dozens are needed, you can use the following calculation:
Number of dozens needed = Total number of students / Students per dozen
Number of dozens needed = 284 students / 12 students per dozen (since a dozen is 12)
Number of dozens needed = 23.67
Since you can't purchase a fraction of a dozen, you need to round up to the nearest whole dozen to ensure that there are enough donuts for every student. So, you would need to purchase 24 dozen donuts for 284 students to receive one each.