Why is this skill important?
Since we expect children of this age to be able to add pairs of numbers without difficulty and with confidence, choosing and using either a mental method for numbers they can add in their heads, or a written method if the numbers are sufficiently large, we need to ensure that they can add two or three single-digit numbers without any problem (see Addition and Subtraction: Skill with single digit numbers). It follows that they will need to transfer this skill to be able to add or subtract multiples of 10 or 100. This is an extension of the addition and subtraction using children’s knowledge and understanding of place value to accomplish it.
Adding multiples of 10 and 100 is crucial to perform written and mental additions. Subtracting pairs of multiples of 10 or 100 is similarly necessary as we come to develop more formal written methods of subtraction in Y5.
What is the skill?
This skill requires the combination of two previous skills that children will hopefully have acquired by this stage.
- Adding several single-digit numbers by spotting pairs to ten and doubles, e.g. adding 5 + 7 + 6 + 3 by spotting that 7+3 is 10 and 5+6 is a near-double (11).
- Understanding that we can count in tens or hundreds or thousands just as we can count in ones, because of the way our number system works.
Putting these two skills together, children can add or subtract multiples of 10, 100 or 1000 without difficulty, e.g. they can see that if 6 + 7 = 13, then 60 + 70 = 130 and 600 + 700 = 1300, etc. Or they can subtract 300 from 800 because they know that 8 – 3 = 5. Children can also add or subtract multiples of 10, 100 or 1000 from or to numbers without having to write these down e.g.
465 – 200 is easy since we know that 4 – 2 is 2. In the same way, 3278 + 600 is simple when we recognise that 2 + 6 = 8.
So the following additions and subtractions become mental calculations rather than written ones using this skill.
- 4672 + 300
- 259 + 40
- 1078 – 500
- 302 + 2000
- 781 – 40
So how is this skill taught?
Since this skill piggy-backs on the two others already mentioned, teachers often ask children to perform trios of related addition or subtraction calculations. The point here is precisely that these sums are in threes.
- 5 + 8 = 13, 50 + 80 = 130, 500 + 800 = 1300
- 14 – 8 = 6, 140 – 80 = 60, 1400 – 800 = 600
- 48 + 20 = 68, 648 + 20 = 668, 6480 + 200 = 6680
- 6 – 5 = 1, 62 – 50 = 12, 362 – 50 = 312
- 2 + 3 = 5, 200 + 300 = 500, 274 + 300 = 574
And so on.
Clearly place value cards (see Number: Place value) can also assist children by helping them to identify the digit that has to be altered in the addition or subtraction.
536 + 200
Separate the cards to show the parts, then change the relevant digit, in this case the hundreds.
When 200 is added, becomes
And the parts can be recombined to give the total
Summarising, this skill is not a difficult one for children to acquire providing the two pre-requisite skills are in place: adding several single-digit numbers by spotting bonds to ten and doubles, and also understanding place value. The actual sums then turn out to be relatively easy and can certainly be done mentally rather than requiring to be written down. This encourages children and helps to improve their mathematical confidence as they wind up doing really big sums in their heads! For example, 7264 – 2000 is really easy-peasy!
Practise Together: These activities are intended to be shared. Read the Explanation of the skill being practised and then play the game or share the task. Watch out for the points highlighted in the Explanation and if necessary, help your child, following the advice in ‘How this skill is taught’ section. Shared activities are not only more fun – they enable you to actively support your child’s learning.
Explanation & Worksheets: Having practised a skill together using the shared activities, children can then rehearse the skill using the ‘Child alone’ sheets. These are presented in order of difficulty 1-5 and should only be given to the child AFTER the Practise Together activities. In this way you can be sure that the child has acquired this skill first. We cannot rehearse what something have not yet learned!
Test: Take a test, questions from this area
Counting in sequence
Read & write numbers
Counting in tens & hundreds
Counting in sequence: Count any sequence of numbers from 1 to 10,000 forward or back with confidence
Read & write numbers: Read and write the numbers 0-10,000
Place value: Understand that 4392 is made up of 4000 + 300 + 90 + 2 and that 4092 has no hundreds
Money: Begin to understand that £6.54 is six pounds and 54 pence and that £6.04 is six pounds and 4p while £6.40 is six pounds and 40p
Counting in tens & hundreds: Count in tens or hundreds forward and back from any number, e.g. 284, 294, 304, 314, etc. understanding how to cross a multiple of 10, 100 or 1000
Count multiples: Count in (add or subtract) multiples of 10, 100 or 1000 (800+300)
Writing fractions: Understand how fractions are written, e.g. ½ and ¾ and begin to realise that ½ is the same as 2/4 or 3/6 etc.
Number Concepts: Count in different ways, understand how numbers work, become fluent in the ways of numbers
Adding and Subtracting: Mentally add or subtract numbers with confidence and develop written ways of adding and subtracting larger numbers or more of them!
Multiplying and Dividing: Know the times tables and use these to perform mental multiplication and divisions; develop written methods for multiplication and division.