Why are numbers even & odd?

We started off the week with the question "What makes an odd number odd and an even number even?" Most of us know that odd numbers are odd if the ones place contains 1,3,5,7,9 and even when there is a 0,2,4,6,8... But what makes them odd/even? We learned two strategies to use when proving that a number is odd or even... the "pair up" strategy and the "divide into groups" strategy. Today we focused on the dividing strategy. Using even and odd numbers of cubes, we tried separating them into two groups to figure out what we noticed about even and odd numbers. We found that even numbers always had an equal number in each group, but odd numbers always had one more in one group. We made a chart with addition sentences to represent our findings.