Learning Objectives
- Count objects from 21 to 50
- Read and write numbers from 21 to 50
- Understand tens and ones in these numbers
- Put numbers in order from smallest to largest
- Skip count by 2s, 5s, and 10s
Key Concepts
Numbers 21 to 50
After 20, we continue counting: 21, 22, 23, and so on up to 50. The number 21 means 2 tens and 1 one. The number 35 means 3 tens and 5 ones. The number 50 means 5 tens and 0 ones. Each number is made up of tens and ones.
Grouping in Tens
We can group objects into tens to count faster. If you have 34 marbles, you can make 3 groups of 10 marbles and have 4 marbles left over. That gives us 3 tens and 4 ones, which is 34.
Counting Forward and Backward
We can count forward: 21, 22, 23, 24, 25, and so on. We can also count backward: 50, 49, 48, 47, 46, and so on. Counting backward helps us with subtraction.
Skip Counting
Skip counting means jumping over some numbers. Counting by 2s: 2, 4, 6, 8, 10, 12, 14, and so on. Counting by 5s: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50. Counting by 10s: 10, 20, 30, 40, 50. Skip counting helps us count large groups quickly.
Comparing Numbers
To compare two-digit numbers, first look at the tens. The number with more tens is greater. If the tens are the same, look at the ones. The number with more ones is greater. For example, 38 is greater than 27 because 3 tens is more than 2 tens.
Important Terms
- Tens place: The digit on the left in a two-digit number shows how many tens
- Ones place: The digit on the right in a two-digit number shows how many ones
- Skip counting: Counting by jumping over numbers in a pattern
- Forward counting: Counting from a smaller number to a bigger number
- Backward counting: Counting from a bigger number to a smaller number
Quick Revision
- Numbers from 21 to 50 are all two-digit numbers
- Every two-digit number has a tens part and a ones part
- Group objects in tens to count faster
- Skip counting by 2s, 5s, and 10s is a quick way to count
- To compare numbers, first compare the tens digit
- 50 = 5 tens and 0 ones, the largest number in this range