Final answer:
Ella needs to purchase 3 bags of hamburger buns to ensure she has at least 20, as each bag contains 8 buns and she cannot purchase half a bag.
Step-by-step explanation:
To determine the number of bags Ella needs to buy for 20 hamburger buns when each bag contains 8 buns, we use simple division. We divide the total number of hamburger buns needed by the number of buns in each bag:
20 buns ÷ 8 buns/bag = 2.5 bags
However, since Ella cannot buy half of a bag, she needs to purchase whole bags. Thus, she will need to buy 3 bags, which will provide her with a total of 24 buns, 4 more than needed, ensuring she has at least 20 buns.