I used to ask kids a lot ofÂ Fermi-type questions — for fun and for them to think about estimation and exponents and problem solving and finding answers to some key questions.

Today’s question is on a much smaller scale than that which is typical of Fermi questions: **How many water balloons would it take to fill up this classroom?**

Now I get to judge which of the six groups’ answers is the “best” one. Their answers were:

1,249

824,256

2,714,166

8,330,800

9,606,908

23,000,000

[According to my calculations, it would take 643,000 water balloons to fill up this classroom. I think we have a winner.]