Americans make 2.3 trips to the grocery store each week. If people
use 5 to 10 bags each time, that's between 600 and 1200 bags per
person per year.
As a class, make two stacks of bags, one paper and one plastic. Use
a ruler to measure the length, width, and height of each stack and
use the 'volume calculator' animation to find out how much space
each stack takes up.