Tens, Ones and Numbers to 120: Grade 1 Study Guide
Place value is the idea that the position of a digit tells its value. It is the key to all later maths.
In Grade 1, children count to 120 and learn that a two-digit number is made of tens and ones. The number 47 is 4 tens and 7 ones. Ten ones can be bundled into one ten, and the number 10 is a special number that makes counting larger numbers efficient.
A great model is a bundle of 10 sticks or a base-ten rod. A rod is worth ten, a small cube is worth one. 47 is four rods and seven cubes. Building numbers with real objects makes the idea concrete before any symbols.
Reading a two-digit number
The left digit counts tens and the right digit counts ones. The number 30 means 3 tens and 0 ones, so you say 'thirty'. The teens (11 to 19) are one ten and some ones: 16 is one ten and six ones.
| Number | Tens | Ones | Expanded |
|---|---|---|---|
| 23 | 2 | 3 | 20 + 3 |
| 60 | 6 | 0 | 60 + 0 |
| 85 | 8 | 5 | 80 + 5 |
| 100 | 10 | 0 | ten tens |
Comparing with greater than, less than
To compare, look at the tens first. 52 is greater than 47 because 5 tens is more than 4 tens. If the tens are equal, look at the ones. 63 > 61. The symbols point to the smaller number: 47 < 52. Many children remember the symbol as an alligator mouth that opens toward the bigger number.
Which number has more tens?
Which has more ones?
>, < or =.
Adding and subtracting tens
Adding 10 to a number changes the tens digit by one: 34 + 10 = 44. Taking 10 away does the opposite: 34 − 10 = 24. A multiple of ten like 20 + 30 is just 2 tens + 3 tens = 5 tens = 50. Adding a one-digit number to a two-digit number: 34 + 5 = 39, since only the ones change unless you cross a ten (38 + 5 = 43).
Worked examples and common mistakes
Example: What is 10 more than 67? 77. Example: Which is greater, 38 or 83? 83. Common mistakes: reversing digits (writing 51 for 15), reading 40 as 'four' only and mistaking 10 more or less for 1 more or less. Ask the child to build the number with rods and cubes to check.
Check your understanding: model answers
1. 5 tens and 6 ones, or 50 + 6. 2. 27 < 72. 3. 80.
✨ Key Takeaways
- A two-digit number is made of tens and ones.
- Compare tens first, then ones.
- 10 more and 10 less change only the tens digit.
- Use bundles, base-ten blocks or a hundred chart.
💬 Questions for Discussion & Reflection
- Write 56 as tens and ones.
- Which is less, 72 or 27? Use a symbol.
- What is 10 less than 90?