I love Sara's blog post about 100#s
I tried it in groups today and the kids loved it. It was so fun. I put up the timer to see how far they could get in 2 minutes. I had 6 groups range from the #20-52.
Then, I told them I was going to now just start the timer to count up to see how much longer it would take us. Surprisingly, it was the group that was at 38 who ended up winning, followed closely behind by 3 more teams right away, all about 2:20 minutes more was needed.
I used the sheet without the quadrants. The team that won did notice the pattern :) Lots of fun. They wanted to try again, but we ran out of time.
Here is the class deep into competition: