# 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.