Fill in the missing number in subtraction sums - at what age?

[ridinghighinapril]

At roughly what age would you expect a child to be able to do sums of this ilk?:

23 - a = 6 or
a - 9 = 3

Thanks

solving 'a', in case it wasn't clear in my previous post

23-?=6 in Y1 ... introducing algebraic equations is touched on in Y4 then covered in upper KS2

Year 2 going into year 3??

My DS does more complicated versions of this. His homework today asked for the factors of 40. I had to google it!!

Year 1 - as an empty box though, not a.

Yes that's why I put ? Not a

I should probably be able to work out how to type a box but I can't be bothered

Thanks, all.
Yes, as an empty box rather than 'a' but couldn't figure out how to do the former on my phone.

DD is in Y1 - she understands that subtraction and division are not commutative but took a while to stop saying, e.g.:
a - 5 = 3, so a = 2

I ended up asking her to write all possible sums for groups of three numbers, e.g.:
7, 2, 9:
7+2 = 9 / 2+7 = 9 / 9-2 = 7/ 9-7 = 2
so she could see the relationship between her number bonds.

The penny has dropped but I wonder if there is a better way (I have also reinforced it without visual representation of the sums)? There is a maths workshop for parents at the start of next month but I don't want to confuse her between now and then.
Thanks again.

Yes best I could do was [] so went for ?

Just realised my paragraph:
"DD is in Y1 - she understands that subtraction and division are not commutative but took a while to stop saying, e.g.: a - 5 = 3, so a = 2"
contradicts itself!
But yes, she does understand she can not take a larger number from a smaller number but then struggled to work out the correct answer.

Your way was exactly right, OP.

AMR123456, once I had "vertex" on the hw and didn't have a clue. I think sometimes teacher expects us parents to know everything!

This online maths dictionary is very handy.