The amount of people in the whole world is pretty wildly unfathomable. For that matter, even a subset like just the 300,000,000 or so that live in the United States can be hard to wrap your head around.
"Paul Hamilton presents iPad tutorials for teachers and parents in school. Relevant for educators who are using ipads in education. This tutorial looks are using App Simple Mind as a mind mapping, concept mapping tool. Appropriate for all year levels from Prep-High School."