seegongsik
Grade 1 (age 6-7)

grade 1 Numbers up to 50

Counting to Fifty

When there are many things, counting one by one gets hard, so grouping them in tens is much faster. 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. Change the tens and ones with the sliders and watch the skip-counting pattern on the number line.

Let's make groups of 10

📦 Why group by 10?
①When you have lots of candies, counting them one by one is easy to mess up
②Put them in groups of 10 and you can just count the groups
③2 groups of 10 is 20, and 3 groups of 10 is 30

Bundling into tens

23
💡 Tens and ones
①Each orange dashed box holds 10 blocks
②The blue blocks are the ones left over
③The numbers under the boxes, 10, 20, 30, go up by 10 with each new box
④23 is 2 tens and 3 ones
⑤The number of tens is the tens digit, and the number of ones is the ones digit

Skip counting by 10s

30up to
🦘 Jumping by 10
①On the number line, the numbers go 0, 10, 20, 30, 40, 50
②Counting like this is called skip counting
③The +10 over each dashed arc is how much one jump adds
④One more jump from 30 lands on 40

Wrap-up

Grouping by 10
tens + ones = total
Groups of 10 make counting quick
Skip counting by 10
10 → 20 → 30 → 40 → 50
Each jump is 10 more
🎯 Remember
①Groups of 10 make counting easy
②Count the tens and the ones, and you have the number
③Skip counting by 10 helps with big numbers
④35 is 3 tens and 5 ones

Examples and unit check

Example 1
There are 3 groups of 10 and 5 loose ones. How many are there in all?
1
3 groups of 10 make 30.
2
Add the 5 loose ones: 30 + 5 = 35.
▸ 35
The number of tens goes in the tens place, and the loose ones go in the ones place.
Example 2
How many tens and how many ones make 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 and ones.
Unit check
What number has 2 tens and 7 ones?
①17
②27
③72
④20
▸ ② 27
1
2 tens make 20.
2
20 and 7 ones make 27.
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Numbers up to 100

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