Add and subtract integers
Home learning focus
Learn about how addition and subtraction can be done in different ways.
This lesson includes:
four interactive practice activities
When writing down sums, separate the numbers into ones, tens, hundreds and thousands. List the numbers in a column and always start adding with the ones first.
- Estimate first and check afterwards - it's a good idea to estimate a rough answer first and then check your actual answer.
- Order doesn't matter - remember that 345 + 129 is the same as 129 + 345.
- Key words - look out for these words in problems: total, sum, altogether, more. They all indicate an addition calculation.
If the numbers are too high or too difficult to subtract in your head, write them down in columns. Separate the numbers into ones, tens, hundreds and thousands. List the numbers in a column and always start with the ones first.
- Estimate first and check afterwards - it's a good idea to estimate a rough answer first. And always check your actual answer.
- Subtraction is the opposite to addition. So subtraction can always be checked by adding. Check that 182 - 37 = 145 by doing the sum: 145 + 37 = 182
- Look out for these words in problems: take away, difference, less than, minus, decrease, fewer than, reduce. They all indicate subtraction.
Adding and subtracting in your head
Rounding numbers to the nearest 1, 10 or 100 can help with lots of mental maths problems.
- To add 9 to another number, add 10 and then subtract 1: 36 + 9 = 36 + 10 - 1 = 45
- To add 18 to another number, add 20 and then subtract 2: 48 + 18 = 48 + 20 - 2 = 66
- To add 97 to another number, add 100 and then subtract 3: 439 + 97 = 439 + 100 - 3 = 536
- To add 0.9 to another number, add 1 and then subtract 0.1: 3.7 + 0.9 = 3.7 + 1 - 0.1 = 4.6
Breaking down numbers
Breaking down numbers can help you add or subtract in your head. For example: find the difference between 38 and 63.
- Count on from 38 to 40 and keep that 2 in your head.
- Now count on from 40 to 60, which is 20.
- Finally count from 60 to 63 which is 3.
- Add them together: 2 + 20 + 3 = 25
Have a go at solving this problem to test your knowledge of addition.
Now have a go at solving this problem to test your knowledge of subtraction.
Try this activity now to test your knowledge of using mental methods.
There's more to learn...
Have a look at these other resources around the BBC and the web.