When there are many things, counting one by one gets hard, so it helps to group them in tens.
Twenty-three is two tens plus three ones, where the number of groups is the tens digit and the leftovers are the ones digit.
That is how a two-digit number is built from tens and ones.
You can also skip-count ten, twenty, thirty to move through big numbers fast.
Here you use the slider to change the tens and ones and watch the skip-counting pattern on the number line.
Let's Group by 10!
📦 Why Group by 10?
①It's hard to count many candies at once
②Grouping by 10 makes it fast!
③Two tens = 20, three tens = 30
Counting in Tens
23
seegongsik.com
Counting blocks grouped in tens
💡 Tens and Ones
①Yellow dashed groups have 10 each
②Blue blocks are leftover ones
③23 = 2 tens + 3 ones
④Try changing the slider!
Skip-Counting by 10
30
seegongsik.com
Number line skip-counting by 10
🦘 Hop by 10!
①10, 20, 30, 40, 50 — grows by 10
②This is called "skip-counting"
③30 + 10 = ? → 40!
④Skip-count up to 50
Summary
Group by 10
tens + ones = total
Grouping by 10 makes counting fast
Skip-count by 10
10 → 20 → 30 → 40 → 50
Each step adds 10
🎯 Remember!
①Grouping by 10 makes counting easy
②How many tens? + How many ones?
③Skip-counting helps with big numbers
④35 = 3 tens + 5 ones
⑤Great job! Ready for 100?
Examples and Unit Test
Example 1
There are 3 tens and 5 ones. How many are there in all?
1
Three tens make 30.
2
Adding the 5 ones gives 30 + 5 = 35.
▸ 35
The number of tens is the tens digit; the number of ones is the ones digit.
Example 2
How many tens and how many ones make up 42?
1
The tens digit of 42 is 4, so there are 4 tens.
2
The ones digit of 42 is 2, so there are 2 ones.
▸ 4 tens and 2 ones
A two-digit number splits into (tens digit) tens and (ones digit) ones.