A key theme of the Common Core State Standards for Mathematics is the need for students to use deeper mathematical thinking and reasoning skills (rather than just memorizing procedures) -- and to apply their understanding of mathematics by justifying conclusions and communicating them to others.

What I think this means is that the Common Core math classroom is going to be a much livelier place, full of discussion and teamwork and talk. That's a wonderful thing.

Here's a fun math conversation starter:

**Which of the following numbers doesn't belong? 9, 16, 25, 43.**

Let us know what you think. And remember, EXPLAIN YOUR REASONING!

## Comments

## 43 - The other numbers can be

## (I apologize for my English

## Isn't it awesome how you can

## 9 doesn't belong, because if

## I say 16 is the number that

## the number that does not

## I'm going to say 16 because

## The number I first looked at

## Sorry for my English, I'm

## 25 doesn't belong because the