Mental addition and subtraction methods

You can add or subtract numbers in lots of different ways.

You can use number lines, number bonds, fact families, 10 squares and counters, or even just writing the numbers down.

Sometimes it is faster and easier to do calculations in your head. This is called mental calculation.

Complete this interactive activity to explore some different methods for addition and subtraction. Then put your knowledge to the test.

It can be quicker and easier to do some calculations in your head.

An easy number to work with could be a single digit number, or a multiple of 10, or a multiple of 100.

This is what these types of numbers look like in a place value chart.

Take a look at this slideshow to see how you can use your knowledge of place value to quickly do this calculation:

4384 + 200 = ?

Using the compensation method

Another way to calculate is to use a compensation method. This method helps if a number is close to a multiple of 10 or 100.

Look at this calculation:

4384 + 190 = ?

It would be easier to add 200 to 4384 than 190.

But if you add 200, you need to compensate by taking 10 away at the end.

The calculations to find the answer would look like this:

4384 + 200 = 4584

4584 - 10 = 4574

This tells you that:

4384 + 190 = 4574

This is what the calculation looks like on a number line:

Counting up to solve subtraction problems

Counting up is a useful method, if you are subtracting two numbers that are close in value to each other.

Look at this calculation:

5125 - 4980 = ?

To solve this you can count up from 4980 to 5000 (which is 20).

Then you can count on from 5000 to 5125 (which is 125).

In total, you will have have counted up 145.

So:

5125 - 4980 = 145