I love a great math task that's open ended, engaging, and easy to use. This one came from a math class I'm taking through my district. It's called "I'm Thinking of a Number." I've included pictures of what I wrote on the board, as well as pictures of what kids did. Two heads are better than one, so they worked in pairs. Here goes...
I'm thinking of a number. My number is between 20 and 40.
Is it 22?
My number is greater than 22.
Is it 33?
My number is less than 33.
Is it 27?
My number is greater than 27.
Is it 31?
My number equals 31.
Thus ensues hooping and hollering!
Needless to say, the kids loved this game. I loved it too. It gave them a change to practice number sense, place value, greater/less than, symbols, cooperation, etc., and it gave me a chance to see who needs more practice with these skills. (Nope, 6 doesn't come between 20 and 40.)
Click on the pictures below for your own copies. A single sheet allows for numbers to 100, because they can use more than two cards to create a number. Obviously the first sheet is more concrete, the second abstract. If you teach larger numbers, add some hundreds to the mix and you're good to go as well.