Number
Place Value: Tens and Units
Junior Infants · Senior Infants · 1st Class · 2nd Class
- ✓By the end of this lesson students will be able to understand that ten units can be grouped to form one 'ten'.
- ✓By the end of this lesson students will be able to identify the 'tens' digit and the 'units' digit in a 2-digit number.
- ✓By the end of this lesson students will be able to represent 2-digit numbers using concrete materials (e.g., bundles of sticks, cubes).
- ✓By the end of this lesson students will be able to read and write 2-digit numbers correctly.
- ✓By the end of this lesson students will be able to understand the value of each digit in a 2-digit number.
Key concepts
Units are single items. We can count them one by one. For example, if you have 7 apples, you have 7 units of apples. The units digit is always on the right side of a number.
When we have ten units, we can group them together to make one 'bundle of ten', or simply one 'ten'. This helps us count bigger numbers more easily. For example, 10 single pencils can be tied together to make 1 bundle of ten pencils. The tens digit is always on the left side of a 2-digit number.
Place value tells us how much a digit is worth based on its position in a number. In a 2-digit number, the digit on the left is in the 'tens place' and tells us how many tens there are. The digit on the right is in the 'units place' and tells us how many single units there are.
A 2-digit number is made up of tens and units. We read these numbers by saying the value of the tens first, and then the value of the units. For example, the number '23' means 'two tens and three units', and we read it as 'twenty-three'.
Key facts to remember
- 1Units are single items.
- 2Ten units can be grouped together to make one 'ten'.
- 3In a 2-digit number, the digit on the left is the 'tens' digit.
- 4In a 2-digit number, the digit on the right is the 'units' digit.
- 5Place value tells us how much a digit is worth based on its position.
- 6We read 2-digit numbers by saying the tens value first, then the units value (e.g., 25 is 'twenty-five').
- 7Numbers from 10 to 99 are 2-digit numbers.
Worked examples
Example 1
Count the total number of stars. Then, group them into bundles of ten and state how many tens and how many units there are.
Answer
There is 1 bundle of ten stars and 5 single stars. So, there is 1 ten and 5 units. The number is 15.
Using physical objects like counters or drawing circles around groups of ten can help visualise this.
Example 2
Represent the number 32 using tens and units. How many tens and how many units are in 32?
Answer
The number 32 has 3 tens and 2 units.
Remember, the '3' in 32 means 'thirty' (3 tens), not just 'three'.
Example 3
Read the number 47 aloud and write down how many tens and units it has.
Answer
The number 47 is read as 'forty-seven'. It has 4 tens and 7 units.
Practice saying numbers like 'forty-seven', 'fifty-two', 'sixty-one' to get used to the sound of tens and units together.
Common mistakes
- ✗Confusing the tens and units digits (e.g., thinking 23 has 3 tens and 2 units).
- ✗Not understanding that a 'ten' is a group of ten 'units', not just the number 1.
- ✗Counting the tens digit as its face value instead of its place value (e.g., seeing the '2' in 23 as two, instead of twenty).
- ✗Incorrectly reading numbers, especially those between 11 and 19 (e.g., reading 13 as 'one-three' instead of 'thirteen').
Exam tips
- ★Always count carefully, especially when bundling items into tens.
- ★Use concrete materials like blocks, counters, or even your fingers to help visualise tens and units if you are allowed.
- ★Remember: the digit on the LEFT is for TENS, and the digit on the RIGHT is for UNITS.
- ★Practice reading 2-digit numbers aloud to get comfortable with their names.
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