Year 5

We can explain each step when we write subtraction calculations in columns using the compact method with whole numbers and up to 2 places of decimals

Year 5 Unit 5b

What we are learning:

We can use the compact method of subtraction for calculations with decimals.

If we have 47.8 – 33.5 we set it out like this:

The decomposition method can also be used with decimals.
49. 6 – 22.7

In this case there were not enough units (6 – 7) so we partitioned the 9 units into 8 units and ten tenths. We have not ‘borrowed’ anything, we have simply used decomposition, or partitioning to break up the top number and write it in a different way so that we can complete the subtraction.

Activities you can do at home:

Try some subtractions using decimals that do not require decomposition like these:
34.7 – 21.2
55.9 – 41.3
99.9 – 44.8

Then try some that do require decomposition like these:
56.1 – 33.9
99.2 – 33.4
71.9 – 59.5

Good questions to ask:

Do we have to use decomposition in this calculation?
If we do, how are we going to partition the top number?
Can you take it away now?

If your child:

Is unsure how to partition decimals
Talk through the fact that decimals behave in just the same way as whole numbers as each column gets ten times smaller as you move to the right, or ten times bigger as you move to the left.