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There are different methods for addition and subtraction.

You may have used column addition and subtraction before but sometimes you can solve additions and subtractions using a mental method.

What is 700-1?

We could use the column method here but that would mean lots of exchanging of 100s, 10s and 1s and lots of crossing out.

It is quicker and just as accurate to just count backwards from 700

700 - 1 = 699

We call this method being efficient which means getting an accurate answer quicker and with less work.

What is 3154 + 300?

We could use column addition to work this out but is there a more efficient method?

Here are the numbers on a place value grid.

The column method would work here but it wouldn't be the quickest way as we only need to think about one column, the hundreds.

We started with 1 hundred and we've added 3 more hundreds.

1+ 3 = 4

so

1 hundred + 3 hundreds = 4 hundreds

Therefore:

3154 + 300 = 3454

You can see from the calculation that only the hundreds digit has changed.

You don't need to draw out a place value grid each time you want to do an efficient addition or subtraction.

Think about what digit is changing and do the calculation in your head.

What is 5616 - 200?

We use the same technique when subtracting.

Which digit will change?

We are subtracting 200 which is 2 hundreds so the hundreds digit will change.

6 - 2 = 4

so

6 hundreds - 2 hundreds = 4 hundreds

Therefore:

5616 - 200 = 5416

This quiz will help you practise adding and subtracting using efficient methods. Remember to think about what is changing in each calculation – the 1s, 10s, 100s or 1,000s?