Terms found in the Everyday Math Unit 1 Lesson

### Commutative Property of Addition

a + b = b + a; two numbers can be added in either order without changing the sum.

### Commutative Property of Multiplication

a X b = b X a; two numbers can be multiplied in either order without changing the product.

### prime number

A whole number greater than one that has only two whole-number factors. 2, 3, 5, 7, 9, 11, 13, 15, 17, ...

### composite number

A whole number greater than one that has more than two factors. 4 has the factors: 1, 4 and 2.

### rectangular array

An arrangement of objects into rows and columns that form a rectangle. All rows and columns must be filled. Each row has the same number of objects. Each column has the same number of objects.

### number model

A number sentence or expression that models a number story or situation.

3 * 4 = 12 Three boys each had 4 marbles.

### factor rainbow

A way to show factor pairs in a list of factors of a number. Can be used to check whether a list of factors is correct.

### divisible by

If the larger of 2 counting numbers, divided by the smaller with no reminder, the larger is divisible by the smaller.

### divisibility rule

A shortcut for determining whether a counting number is divisible by another counting number without actually doing the division.

### turn-around rule for multiplication

A rule for solving addition and multiplication problems based on the Commutative Properties of Multiplication and Addition. For example: if you now that 6** 8= 48, then by the turn-around rule you also know that 8 ** 6 = 48.

### factor string

A counting number written as a product of two or more of its counting-number factors other than 1. The length of the factor string is the numbers in the string. 2**3**4 is a factor string for 24 with length 3.