- Read and write two-digit numbers
- Split a number into tens and ones: 47 = 40 + 7
- Compare two-digit numbers
At the market, Grandma packs eggs into boxes of 10. She filled 4 boxes and 7 eggs are left over. How many eggs are there? 47! In this lesson you will find out how numbers up to 100 are built from tens and ones.
Counting in tens
Let's count in tens: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100. These numbers all end in 0: they are whole tens. Ten tens make one hundred: 100 = 10 tens.
A number written with two digits. The left digit shows the tens, the right digit shows the ones. 47 has 4 tens and 7 ones: 47 = 40 + 7.
Every digit has its place
| Number | Tens | Ones | As a sum |
|---|---|---|---|
| 47 | 4 | 7 | 40 + 7 |
| 36 | 3 | 6 | 30 + 6 |
| 63 | 6 | 3 | 60 + 3 |
| 70 | 7 | 0 | 70 + 0 |
Samir has 3 boxes with 10 coloured pencils in each, and 8 more pencils. How many pencils does Samir have in all?
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30 + 8 = 38.
Samir has 38 pencils: 3 tens and 8 ones.
a) 6 tens and 0 ones.
b) 9 tens and 9 ones.
c) The number that is 1 more than 99.
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b) 9 tens and 9 ones = 99.
c) 99 + 1 = 100: ten tens make one hundred.
Comparing two-digit numbers
First compare the tens: the number with more tens is bigger. If the tens are the same, compare the ones.
a) 58 and 61.
b) 74 and 72.
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So 58 < 61, even though 8 > 1.
b) Both have 7 tens. Compare the ones: 4 > 2.
So 74 > 72.
Let's practise
- 1.40 + 7 =
- 2.60 + 3 =
- 3.58 = 50 +
- 4.35 + 10 =
- 5.72 − 10 =
- 6.39 + 1 =
- 7.70, 80, 90,
- 8.83 38
- 9.46 49
Key points
- 10 ones = 1 ten, and 10 tens = 1 hundred (100).
- In a two-digit number, the left digit is the tens and the right digit is the ones: 47 = 40 + 7.
- To compare, look at the tens first and then at the ones.
- Adding or taking away 10 changes only the tens digit.
Check yourself
10 questions. Every correct answer earns XP.