D

decimal

A number written using the base-ten place value system and containing a decimal point. For example, 7.25 is a number written as a decimal. (See also decimal fraction.)

pages 454–462, 463–465, 466–473, 481, 482–486

decimal fraction

A fraction written as a decimal. For example, 0.75 and 0.4 are decimal fractions and and are called common fractions.

pages 454, 456, 459–464, 466–468, 471–473

decimal hopper

Like base-ten hoppers, decimal hoppers can hop only distances based on base-ten place value units, but now the rule extends into decimal fractions as well. Decimal hoppers can hop a distance of 0.1, 0.01, or 0.001.

pages 482–486

decimal point

A period between the whole units and the decimal places in a number. The numbers to the right of the decimal point are less
than 1.

pages 454, 459, 468

decimeter

A unit of length in the metric system. A decimeter is of a meter.

pages 449, 451–452, 454

decrease

To go down in value. In a line graph with decreasing values, the line slants downhill as you read the graph from left to right.

page 575

degree

A degree (°) is a unit of measure for angles. There are 360 degrees in a circle.

pages (temperature) 183, (angle measure) 381–383, 386, 389, 391, 397, 399–401

denominator

The number below the line in a fraction. The denominator indicates the number of equal parts in which the unit whole is divided. For example, 4 is the denominator of the fraction . (See also numerator.)

pages 298, 302, 304, 307–308, 317, 320, 323, 325, 327, 329, 332–333, 340, 345, 351, 362, 363, 454, 463–464, 466

dependent variable

The variable whose value results from the experiment. Experimenters find the values of the dependent variable by doing the experiment. The dependent variable is often called the responding variable.

distributive property

The distributive property of multiplication over addition states:

a × (b + c) = (a × b) + (a ×c) or
4 × (3 + 2) = (4 × 3) + (4 × 2).

dividend

The number that is divided in a division problem; e.g., 12 is the dividend in 12 ÷ 3 = 4. 3 is the divisor and 4 is the quotient.

pages 73, 530, 546–547, 549

divides evenly

When you divide a whole number by one of its factors, the answer (or quotient) is a whole number with no remainder. For example, 3 divides evenly into 27 since 27 divided by 3 equals 9.

page 258

divisible

A number a is divisible by a number b, if there is no remainder when a is divided by b. For example, 12 is divisible by 4 (12 ÷ 4 = 3), but not by 5 (12 ÷ 5 = 2 R2).

pages 257–263

division

The operation of making equal groups. For example, there are 3 groups of 5 in 15.

pages 73–77, 214–219, 528–529, 530–534, 535–540, 541–543, 544–546, 546–552

division sentence

A number sentence involving division.

pages 72–74, 82, 258–262

divisor

In a division problem, the number by which another number is divided. In the problem 12 ÷ 4 = 3, the 4 is the divisor, the 12 is the dividend, and the 3 is the quotient.

pages 73, 215–216, 530, 546–547

doubling

Making something twice as big, e.g., adding a number to itself or multiplying a number by two: 6 + 6 = 12 or 6 × 2 = 12.

pages 154, 207–209, 214, 224–225, 518, 525

duplation

Multiply by doubling.

page 513