Check each sum first: is it plus or minus?
Subtraction to 20
Subtraction to 20 practice, from 19 − 2 to 12 − 7 = 5: first without crossing ten, then back across ten, then three or four numbers, plus and minus mixed.
Your child can start here once they can add within 20 and subtract within 10; the later exercises, with plus and minus mixed, also need adding to 10. Going back across ten takes two jumps, for 12 − 7 back 2 to reach 10 and then 5 more, and a child who has to stop and work out how 7 splits into 2 and 5 loses the thread halfway.
Usually taught in Year 1–2 in England and Wales, around ages 5 to 7. Every child goes at their own pace; this is a guide, not a requirement.
The first of 28 exercises in this topic. See them all
What it looks like for your child
With one exercise from this topic as the example: Crossing ten.
1
2
3
4
How it fits together
The arrows point to what can be done next. Whatever sits inside a box belongs to it.
Subtraction
Subtraction to 20
Two numbers to 20
More numbers and balance to 20
Can come next
first this, then that belongs to
Read the whole sum before you fill in: is something added, or taken away?
30 sums in a row, everything mixed: the real test.
A race against time, for children who can already do it and want to be faster.
Left to right, one step at a time.
Work out one side, then make the other side the same.
60 sums in a row, everything mixed: the real test.
Two numbers to 20
17 − 5: just the ones, 7 − 5 = 2, so 12.
Back to the ten first: 13 − 5 = 13 − 3 − 2 = 8.
Turn it round: 17 − ? = 12 is the same as 12 + ? = 17.
Count up from the small number: 20 − 7 — from 7 to 10 is 3, then 10 more, so 13.
Turn it round: 13 − ? = 8 is the same as 8 + ? = 13.
Look first: can you take the ones away without going back past ten?
Which two numbers give this difference? Tap them in the right order.
More numbers and balance to 20
Take them away one at a time, left to right.
Work out one side, then make the other side the same.
Work out what is already there first, then see how much is missing.
One minute, as many sums as possible. Not needed to move on, but good for getting quicker.
Take them away one at a time, left to right.
Against the clock: how many can your child do in sixty seconds?
Work out what is already there first, then see how much is missing.
Mixed to 20
The same sum as 13 − 5 = 8, but ten times bigger: 130 − 50 = 80.
Against the clock: how many can your child do in sixty seconds?
The same sum as 13 − 5 = 8, but a hundred times bigger: 1300 − 500 = 800.
Just like 20 − 6 = 14, but ten times bigger: 200 − 60 = 140.
The same sum as 13 − 5 = 8, but a thousand times bigger: 13000 − 5000 = 8000.
Just like 20 − 6 = 14, but a hundred times bigger: 2000 − 600 = 1400.
Just like 20 − 6 = 14, but a thousand times bigger: 20000 − 6000 = 14000.
Why it matters
This is the big new step in subtraction: going back across ten. In 16 − 3 the ones simply stay within the ten, but in 16 − 9 your child has to go back past 10. That is a different action, and the exercises keep the two kinds apart at first before they are mixed.
A child who really masters this step holds the key to all the subtraction that comes after. In 46 − 9 or 83 − 7 exactly the same thing happens, just a few tens higher. So this is not only about working up to 20; it lays down a method.
How to approach it
The handiest route goes in two jumps: first back to ten, then take away the rest. For 14 − 6, take away 4 first, which brings you to 10, and then 2 more, so 8. Your child does need to know that 6 can be split into 4 and 2; this is where the number bonds to 10 come in useful again.
When the numbers are close together, as in 12 − 9, counting up is quicker: from 9 to 12 is 3. Encourage your child to look first at which of the two routes is shorter for each sum. The ‘Crossing ten or not’ exercise is all about that moment of looking.
When is it secure?
A round of 10 sums in one go without a mistake, within 30 seconds. That is about 3 seconds a sum: no more counting, just knowing.