A

abacus

A counting board made of rods and beads.

pages 171–183

addend

The numbers that are added in an addition problem are called the addends. For example: 4 + 9 + 6 = 19. 4, 9, and 6 are called addends.

page 19

addition

The operation of finding the total of two or more numbers (e.g., 45 + 7 = 52).

pages 16–18, 136–139, 140–145, 146–147, 184–187

all-partials method

A paper-and-pencil method for solving addition and multiplication problems. Each partial sum or product is recorded on a separate line.

page 141

angle

The amount of turning between two rays that have the same endpoint.

pages 307, 311, 321

apex

The top vertex of a pyramid or cone.

area

The area of a shape is the amount of space it covers, measured in square units.

pages 99–100, 104–120, 121, 129–130

array

An array is an arrangement of objects into a rectangular pattern of (horizontal) rows and (vertical) columns.
(See also column and row.)

associative property

The change in grouping of three or more addends or factors does not change their sum or product.

average

A number that can be used to represent a typical value in a set of data.
(See also mean, median, and mode.)

axes

Reference lines on graphs and grids. The axes are two perpendicular lines that cross at the origin or zero. The singular of axes is axis.

pages 4, 5, 6, 10, 22, 324–326, 340