# 2.4 Addition and Subtraction on the Number Line

## Unit Goals

• Students learn about the structure of a number line and use it to represent numbers within 100. They also relate addition and subtraction to length and represent the operations on the number line.

### Section A Goals

• Represent whole numbers within 100 as lengths from 0 on a number line.
• Understand the structure of the number line.

### Section B Goals

• Represent sums and differences on a number line.

### Glossary Entries

• bar graph
A way to show how many in each group or category using the length of rectangles.

• centimeter

A length unit in the metric measurement system. There are 100 centimeters in a meter.

• compose
To make a new unit from 10 of the next smallest unit. For example, compose a ten from 10 ones.

• data
Information about the things or people in a group.

Example: If you have a box of colored pencils, then the lengths and colors of each of the pencils are data about the pencils in the box.

• decompose
To break a unit into 10 of the next smallest unit.  For example, decompose a ten into 10 ones.

• foot

A length unit in the U.S. customary measurement system.

There are 12 inches in a foot.

• inch

A length unit in the U.S. customary measurement system.

There are 12 inches in a foot.

• line plot
A way to show how many of each measurement using an x for each measurement.

• meter

A length unit in the metric measurement system.

There are 100 centimeters in a meter.

• number line

A diagram that represents numbers as lengths from 0 using equally spaced tick marks or points.

• picture graph
A way to show how many in each group or category using pictures of the objects or symbols.