Horizontal addition - how is it done?

[ridinghighinapril]

DD will be learning this method soon and I am not remotely familiar with it but would like to be so I can help her.
How would I, for example, calculate:

• 13 + 27
• 235 + 723
• 1764 + 784?

Thanks!

Number line?

I think you mean a method whch lays out the numbers underneath each other making sure the units, tens and hundreds are lined up.

I like to start with an old fashoined method of heading up the sum with

H T U
then you can put the numbers underneath

H T U
1 3 +
2 7

Th H T U
1 7 6 4 +
7 8 4

13+27would normally be initially taught to start from 27 and count on 13

But there are a number of ways it could be approached
10+20 +7+3
27+3+10

My ds's school made maths calculation booklet for parents explaining which method they use and how they do it.( as a small booklet and on their website as well.)
Maybe ask your dc's teacher if they have one as well? It is very handy since there are lots of different methods and different names for same method.