Calculating
Adding and subtracting two 2-digit numbers
In this unit you add two 2-digit numbers and subtract one 2-digit number from another. You also find the difference between two numbers. The trick is to work with the tens and the ones.
Adding two 2-digit numbers
Split each number into tens and ones. Add the tens, then add the ones, then put them back together. Example: 21 + 47. Tens: 20 + 40 = 60. Ones: 1 + 7 = 8. So 60 + 8 = 68.
Subtracting a 2-digit number
Split each number into tens and ones. Subtract the tens, then subtract the ones, then put them back together. Example: 67 - 32. Tens: 60 - 30 = 30. Ones: 7 - 2 = 5. So 30 + 5 = 35.
Finding the difference
The difference is how far apart two numbers are. To find it, take the smaller number away from the bigger number. Example: the difference between 49 and 32 is 49 - 32 = 17. You can also count on from 32 to 49.
Worked examples
Add two 2-digit numbers
- Split into tens and ones: 21 is 20 and 1, 47 is 40 and 7.
- Add the tens: 20 + 40 = 60.
- Add the ones: 1 + 7 = 8. Put them together: 60 + 8.
Answer: 21 + 47 = 68
Subtract a 2-digit number
- Split into tens and ones: 67 is 60 and 7, 32 is 30 and 2.
- Subtract the tens: 60 - 30 = 30.
- Subtract the ones: 7 - 2 = 5. Put them together: 30 + 5.
Answer: 67 - 32 = 35
Find the difference
- The difference is the gap between 49 and 32.
- Take the smaller from the bigger: 49 - 32.
- Tens: 40 - 30 = 10, ones: 9 - 2 = 7, so 10 + 7.
Answer: The difference between 49 and 32 is 17.
Where you see this in real life
- Adding two prices to find the total cost of two toys.
- Working out how many are left after you take some away.
- Finding the difference between two scores in a game.
- Adding the number of children in two classes.
Key words
- 2-digit number
- A number with a tens digit and a ones digit, such as 47.
- Tens
- The tens digit tells you how many tens, for example the 4 in 47 means 40.
- Ones
- The ones digit tells you how many ones, for example the 7 in 47 means 7.
- Total
- The answer when you add numbers together.
- Difference
- How far apart two numbers are, found by taking the smaller from the bigger.