If a helium balloon pops in a room, how long will it take the helium to thoroughly mix with the air in the room (assuming no air currents)? (Thanks to Sebastian Kuhn of Old Dominion University for suggesting the question.)
How many pennies would it take to cover the United States? How many to cover just your state? (Thanks to Scott Chan, American High School, Fremont, CA, for suggesting the question.)
Look for the answers online at tpt.aapt.org. Question suggestions are always welcome! For more Fermi questions and answers, see Guesstimation 2.0: Solving Today’s Problems on the Back of a Napkin, by Lawrence Weinstein (Princeton University Press, 2012).
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