It is a given that Mrs. Kennedy can not purchase half a pack of pencils, however, she needs 315 pencils for each student. Because you can not achieve the product 315 by multiplying by 10, Mrs. Kennedy will have to round up in order to have enough pencils for each student. Rounding up to the nearest ten, your result would be 320. With this number, Mrs. Kennedy can determine that she should purchase 32 packs of pencils, as each pack contains 10 pencils, and she would need at least 320 to meet her requirement.