Year 3 son struggles with subtracting 10

[confusedinlondon]

My son was exceeding maths in year 1 not sure whats happened but he is struggling now.
He really struggles with subtracting when going past a hundred. 300-7 he will say 203. Even 205- 10 he wont be able to work out unless he uses his fingers and even then he'll go wrong.
Any idea how i could help him. I have brought cubes and things.
Any books i could buy? Cgp or white rose maths books.

He'll get there in the end, what age is this taught in the school curriculum where you are ?

Oh sorry I misread your post

He has missed big chunks of his learning due to the pandemic. A lot of year 3 children are struggling at the moment. The CT will work on this. He is not alone.

He needs to see it practically. Something like dienes/base 10 blocks might help . Mathsbot have lots of free virtual maths manipulatives.
mathsbot.com/manipulativeMenu
mathsbot.com/manipulatives/blocks

There are lots of subtraction with manipulatives clips on youtube for eg.

Also make sure he understands what is one less than 300, 200 etc then 2 less etc. For the 205 question I would suggest using number bonds to 10. Take away 5 to get to 200 first. Then take away the other 5 from 200.

The starting value of the mathsbot hundred square can be changed so you can explore numbers either side of 100,200, 300, etc. Often children are familiar with a 100 square but cannot visualise numbers beyond. mathsbot.com/manipulatives/hundredSquare
It is easier to see how numbers work when the physically making the "100 square". You could start of writing numbers on cards from say for e.g. 180 to 220 . Lay the 180 to 189 cards down like a hundred square and get your son to continue making with the 190 beneath the 180 etc. Then its easier to see what happens when numbers go over hundreds.

Maths games are also a brilliant way to build up confidence in maths in a fun way. It is worth looking on pinterest to find games that will appeal to your child.

Can he subtract crossing a tens boundary not a hundreds boundary. So 65-10 or 80-7? Try getting him to think about what strategies he uses to do that and spending time counting forwards and backwards across the hundreds boundaries.

If he’s completely confident with both those things then go with using base 10/ diennes to help him see what’s going on.

Using coins and practice helped DS with that kind of place value question. I use just 1p, 10p and one pound coins, and then get him to practice a few sums / write a few for me to make.

This happens when kids don’t have a solid understanding of number based and how numbers are made up in general.
I second the post that said you should get base 10 materials - they look like that….
Then take an A4 paper and draw three columns - Hundreds I Tens I Ones
Show him how 305 is represented —
Lay out three of the hundreds squares into Hundreds column, and five little ones into the Ones column
Then ask him how he can take 10 ones out if that number.
Repeat it with different numbers, and with practice he’ll hopefully start getting it.

This is quite an important concept to grasp as he’ll need it as a basis for future learning.

Thanks all. He is fine with 82-6 type questions, although he will count back using his fingers rather than 82-2 =80 - 4 = 76. If i sit with him and go through the process.
He is fine doing subtraction via the colum method, its just here he reverts to saying 300 - 7 is 203 rather than 293

“ just here he reverts to saying 300 - 7 is 203”

That’s like he’s not seeing the zero in the middle. He’s not seeing the full thing, only 30-7=23. But he knows there should be a third zero so bungs it in the middle and hopes for the best.

I’d be tempted to go back to working with place value, numbersense and mental Subtraction with 2-digit numbers.

Nothing wrong with counting back, but if it’s the only strategy he has it might well be covering up for a lack of understanding. Better to focus on this before trying to apply the same understanding to larger numbers.

If you look on the school website, you might find their calculation policy. It’s often under the ‘curriculum’. This should tell you what strategies they teach for Subtraction.

He really struggles with subtracting when going past a hundred. 300-7 he will say 203. Even 205- 10 he wont be able to work out unless he uses his fingers and even then he'll go wrong.

Use 10p coins or dienes to make 100/200/300 to establish that 10 10s equals 100.

Make 205 using 10p coins & 5 1ps. Ask him to take 10 away ie a 10p coin) then count what's left. Repeat lots of times with different amounts but always taking away 10. He should start to see what happens.

Make 300 with 10s & ask him to take away 7. He will need to exchange a 10 for 10 1s begore he can do it.

Have a look at the white rose home learning videos for year 3 place value.

He really shouldn’t be doing column additions/subtractions. He can only do it mechanically without proper understanding.

You really need to go back to place value and make sure that he gets how numbers are made. Ed
That 86 is made up of eight 10s and 6 ones
That 234 is made up of two 100s and three 10s and 4 ones
Etc

Without this basic understanding being automatic in his head - he’ll struggle later in his school math.
Currently he seems to only know how to count up or down. It’s fine for small numbers, but doesn’t work for big ones.

It’s not a difficult concept to reach. If you don’t want to buy extra materials - make cards with 100, 10, 1 . Ask him to make up different numbers. Ask him to use those to aid in additions/subtractions.
Then add cards with a 1000 in there and see if he gets the concept.

Thanks - you are all right. I have been doing place value with him and asking him to count back from 00 and forward from 00 and he sometimes gets confused.
I have been using base 100 and 10.

This is good. I would NOT practice counting on at this stage. He already relies on that method too much.
He needs to understand that adding/subtracting is NOT just counting this or they way.

If you use coins or make cards - you can show him visually how to take/add parts of numbers. Like you cut a chunk of a chocolate bar, for eg. You aren’t cutting it off but by bit, you take a part off.
If you have physical representation of a number with some aid it’s easier to show.