T

tally

A way of recording a count by making marks. Tallies are usually grouped in fives.

ten frame

A rectangle made up of two rows of five. Ten frames can help students count, add, subtract, and group numbers.

tens

1. The whole numbers that are two digits long (10–99).
2. The second place or column from the right is called the tens place. For example, in the number 215, the 1 represents 1 ten.

thinking addition

A strategy that uses an addition fact you know to solve a subtraction problem. For example, 15 − 7 = 8 because 8 + 7 = 15.

thirds

Three parts of a whole that are the same size. (See also fair share and one-third.)

thousand

The number 1000 or ten 100s.

three-dimensional (3-D)

An object that has length, width, and height like objects in the real world.

three-fourths

Three-fourths is three pieces of a whole or group divided into four equal parts or four "fair shares." (See also fair share, fourths, and one-fourth.)

TIMS Laboratory Method

A method used to organize experiments and investigations. There are four steps: draw, collect, graph, and explore. It is a way to help students learn about the scientific method.

tool

An object or device used to develop math skills for counting, adding, subtracting, or representing numbers. For example, number lines, ten frames, beans, and connecting cubes are tools to help solve math problems.

total

The whole amount; the sum of two or more numbers.

trade

Regrouping or exchanging one item for another. For example, when using the Fewest Pieces Rule, if you have 12 bits, you trade 10 bits for one skinny. (See also Fewest Pieces Rule.)

trapezoid

1. A two-dimensional (2-D) shape with exactly one pair of parallel sides.

2. A two-dimensional (2-D) shape with at least one pair of parallel sides.

trial

One test or "try" in an experiment.

triangle

A two-dimensional (2-D) shape with three sides and three corners.

triple

Three times as much or as many.

true number sentence

A number sentence in which the numbers on both sides of the equal sign have the same value.

3 + 4 = 2 + 5 is a true number sentence.
3 + 4 = 8 is not a true number sentence.

turn-around fact

Addition or multiplication facts that have the same numbers but in a different order, For example, 3 + 4 = 7 and 4 + 3 = 7, 3 x 4 = 12 and 4 x 3 = 12. (See also commutative property of addition and
turn-around rule.)

turn-around rule

Changing the order of the numbers in addition or multiplication does not change the answer. For example, 3 + 4 = 7 and 4 + 3 = 7, 3 x 4 = 12 and 4 x 3 = 12. (See also commutative property and
turn-around fact.)

two-dimensional (2-D)

A shape having length and width but no thickness.

two-pan balance

A tool for measuring the mass of an object by balancing the object in one pan and a number of standard masses in the other pan.