Divisibility rules, prime numbers (and review of place value) Here's a couple of riddles. I'll enlarge them to poster size, put them up on the math bulletin board, and offer a prize to the first one to solve it. They are from our math curriculum director. She didn't give me the answer, so I hope I've got them correct. Number Riddle #1 I am a 4-digit number with a decimal between 400 and 650. My hundreds digit is divisible by 2 but not by 3. My tens digit is a multiple of 3. My ones digit is ½ of my tens digit. All of my digits are different. The sum of my digits is 20. What number am I? (463.7) Number Riddle #2 I am a 2-digit whole number between 30 and 80. My tens digit is one more than my ones digit. I am a prime number. What number am I? (43) Number Riddle #3 I am a 4-digit whole number greater than 6000. My thousands digit is prime. My ones digit is the only even prime number. I am divisible by 4. My tens digit is ½ of my hundreds digit. All of my digits are different. What number am I? (7632)

Oooh, I like those!! Especially for my kids who understand the math quickly, and are staring off into space while I am going over the concept again for those who are still not sure! They can be reading these posters and trying to figure them out! One strategy I have used in the past is to make the Everyday Math games a center.Once a week, I pull out all the games. The kids pick a game, and then they "teach" themselves how to play. I usually do not introduce games until the concepts have been covered, but occasionally some of my top math kids want to try to figure it out. They really love this, even in 5th grade-centers are a hit!!!!!!!!

On the day before Thanksgiving, I gave each of my Algebra I classes 4 brainteasers http://www.braingle.com/Logic-Grid.html I told them they could work alone or in groups, but I wanted one right answer per class. If I got it, there would be extra credit for every member of that class. Three of my classes got the extra credit, and it was a nice relaxing break before the holiday.

That's a great link, Alice--I've just bookmarked it. I have to cover a grade 8 math class once a month or so and the teacher often leaves it up to me to decide what to do because he feels that I don't "need" him to leave me a plan (but that's a whole other story). Some of these will come in handy.

I do an idea silimar to the riddle idea from th efirst poster. I start a apiral bound notebook. I write in a riddle each day for a week. During math I read it aloud and write it on the board. I give students until the following day to answer, then we go over it. I then send the notebook home with each student for one night. they must create and write a riddle for the class to solve. When they return to school, they write it on the board, correct student responses, and lead the class in solving the riddle. They love this!

OK Braingle and Mr. K's idea are good! I did get a few off Braingle, but having the kids come up with some will help. Is it one kid writing the riddle for the next day?