Number & Operations in Base Ten
Understanding Place Value to 120
Grade 1
- ✓By the end of this lesson students will be able to identify the tens and ones digits in a two-digit number.
- ✓By the end of this lesson students will be able to represent a number up to 120 using tens and ones.
- ✓By the end of this lesson students will be able to compare two two-digit numbers using the symbols >, <, or =.
- ✓By the end of this lesson students will be able to explain how the position of a digit affects its value.
Key concepts
Place value tells us how much each digit in a number is worth based on its position. In numbers up to 120, we mostly focus on the 'tens place' and the 'ones place'. The digit on the right is in the ones place, and the digit to its left is in the tens place.
Every two-digit number is made up of a certain number of 'tens' and a certain number of 'ones'. For example, the number 34 has 3 tens and 4 ones. We can think of 1 ten as a bundle of 10 ones. So, 3 tens is the same as 30 ones. When we write a number like 72, the '7' is in the tens place, meaning 7 tens (or 70), and the '2' is in the ones place, meaning 2 ones.
To compare two-digit numbers, we first look at the digit in the tens place. The number with more tens is the greater number. If both numbers have the same number of tens, then we look at the digit in the ones place. The number with more ones will be the greater number. We use special symbols to show our comparison: '>' means 'is greater than', '<' means 'is less than', and '=' means 'is equal to'.
Key facts to remember
- 1The ones place is the digit on the right.
- 2The tens place is the digit on the left in a two-digit number.
- 3One 'ten' is the same as 10 'ones'.
- 4To compare numbers, first look at the tens digit.
- 5If the tens digits are the same, then look at the ones digit.
- 6The symbol '>' means 'is greater than'.
- 7The symbol '<' means 'is less than'.
- 8The symbol '=' means 'is equal to'.
Worked examples
Example 1
How many tens and ones are in the number 58?
Answer
The number 58 has 5 tens and 8 ones.
Remember, the digit on the left tells you the number of tens, and the digit on the right tells you the number of ones.
Example 2
Write the number that has 7 tens and 3 ones.
Answer
The number is 73.
You can think of 7 tens as 70, and then add 3 ones: 70 + 3 = 73.
Example 3
Compare 62 and 26. Use >, <, or =.
Answer
62 > 26
Always start by comparing the tens digits first! If they are the same, then compare the ones digits.
Common mistakes
- ✗Confusing the tens and ones digits (e.g., saying 23 has 3 tens and 2 ones).
- ✗Only looking at the ones digit when comparing numbers (e.g., thinking 31 is greater than 40 because 1 is less than 0).
- ✗Incorrectly using the comparison symbols (e.g., writing 5 < 2 when it should be 5 > 2).
- ✗Not understanding that '1 ten' is a group of 10 individual units.
Exam tips
- ★Always read the number carefully to identify which digit is in the tens place and which is in the ones place.
- ★When comparing numbers, draw or imagine base-ten blocks to help visualize the amounts.
- ★Practice writing numbers from 1 to 120 and identifying their tens and ones.
- ★Remember the 'alligator mouth' trick for comparison symbols: the open mouth always 'eats' the bigger number.
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