Compare unit rates — rebuild the idea
Follow-up task
For identical erasers with no fees, box A costs 10 dollars for 5 erasers; box B costs 12 dollars for 3 erasers. Make two labeled rows with a column for dollars per 1 eraser. Divide both quantities in each row by its eraser count. Which unit cost is lower? Why is 10 dollars versus 12 dollars not enough reasoning?