Progression in written Progression in written methods for subtractionmethods for subtraction

NNS recommendations

Stage 1: counting up from the smaller to the larger number

I can find 84 - 56. Watch!

56 + 4 + 20 + 4 = 84. So 84 – 56 = 28.

Stage 2: compensation

Here we take too much then add back.

84 - 56 is the same as 84 – 60 + 4 which is 24 + 4 = 28!

Stage 3: use of the expanded subtraction algorithm (no decomposition required)

This stage is the beginning of the standard algorithm but in a much expanded format. As no decomposition is required, the calculation can be done left to right.

I understand how this method works!

563 – 241 = 500 + 60 + 3

- 200 + 40 + 1

300 + 20 + 2

So 563 – 241 = 322

Stage 4: use of the expanded subtraction algorithm (decomposition required)

This is a bit more difficult. I

have to exchange 1

hundred for 10 tens and 1 ten for 10 units!

566 – 278 = 500 + 60 + 6 = 400 + 160 + 6

- 200 + 70 + 8 - 200 + 70 + 8

= 400 + 150 +16

- 200 + 70 + 8

200 + 80 + 8 = 288

Stage 5: standard method

The standard contracted algorithm is used using decomposition where necessary.

I understand how to use this

method because really it is the same

as the last method we

used!

566 – 278 = 51616 - 2 7 8 2 8 8