If she wants each student to have 1 ice cream sandwich, she should buy 2 boxes to have a total of 20 ice cream sandwiches. You cannot buy half of a box, so therefore you would have to buy 2 boxes to have a total of 20 ice cream sandwiches if you want each student to have 1 ice cream sandwich.
Well since there are more than 10 people she should first get one box. She will then have 5 more people to feed so she will just have to buy another even though there will be leftovers.
