Learning Objectives
- Count forward and backward in tens
- Understand place value of tens and ones
- Read and write two-digit numbers correctly
- Add and subtract multiples of 10
- Represent numbers using bundles and loose sticks
Key Concepts
Counting by Tens
When we count by 10s, we say: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100. Each of these numbers is made up of only tens and zero ones. 10 is 1 ten, 20 is 2 tens, 30 is 3 tens, and so on. Counting by tens is a quick way to count large groups of objects.
Tens and Ones
Every two-digit number has a tens part and a ones part. The number 36 has 3 tens and 6 ones. The number 52 has 5 tens and 2 ones. The number 80 has 8 tens and 0 ones. We can show this with bundles of sticks: 3 bundles of 10 sticks and 6 loose sticks make 36.
Expanded Form
We can break a number into its tens and ones. This is called expanded form. For example: 45 = 40 + 5, 73 = 70 + 3, 91 = 90 + 1. The expanded form helps us understand what each digit in a number means.
Adding Tens
Adding tens is easy. 20 + 30 = 50 (just add 2 + 3 = 5 tens). 40 + 10 = 50 (4 + 1 = 5 tens). When we add tens to a number, only the tens digit changes. For example, 34 + 20 = 54.
Subtracting Tens
Subtracting tens works the same way. 50 − 20 = 30 (5 − 2 = 3 tens). 80 − 30 = 50 (8 − 3 = 5 tens). When we subtract tens from a number, only the tens digit changes. For example, 67 − 30 = 37.
Important Terms
- Tens: Groups of ten objects
- Ones: Single objects not in a group of ten
- Place value: The value of a digit based on where it is in the number
- Expanded form: Writing a number as the sum of its tens and ones (e.g., 56 = 50 + 6)
- Two-digit number: A number from 10 to 99 that uses two digits
Quick Revision
- Count by 10s: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100
- Every two-digit number = tens + ones
- Expanded form of 48 = 40 + 8
- Adding tens: 30 + 40 = 70
- Subtracting tens: 90 − 50 = 40
- Use bundles of sticks to show tens and loose sticks for ones