# 1.3 Adding and Subtracting Within 20

## Unit Goals

• Students add and subtract within 20. Students apply the properties of operations and the relationship between addition and subtraction.

### Section A Goals

• Build toward fluency with adding and subtracting within 10.

### Section B Goals

• Add and subtract one-digit numbers from teen numbers without composing or decomposing a ten.
• Find the value that makes an addition or subtraction equation true, involving 10.
• Understand 10 ones as a ten and the numbers 11 to 19 as a ten and some ones.

### Section D Goals

• Subtract within 20.

### Glossary Entries

• category
A label that tells how objects in a group are alike.

• 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.

• difference
The result when one number is subtracted from another.

• sum
The total when two or more numbers are added.

• survey
A way to collect data using a group of people answering the same question.

• teen number

A number with 1 ten and between 1 and 9 ones.

Example:
Fifteen is 1 ten and 5 ones.