For semi-written calculation you split the numbers into tens and ones.
Example: 341 + 256 split up
341 + 256 = 340 + 250 + 1 + 6
= 590 + 7
= 597
The numbers written in show the answer.
Example
341 + 256 =
= 340 + 250 + 1 + 6
= 590 + 7
= 597
173 + 524 =
= 170 + 520 + 3 + 4
= 690 + 7
= 697
For parents
What does this exercise practice?
This exercise strengthens place value understanding with bigger numbers too and shows a flexible way of calculating before the written method comes.
Common pitfalls
Children sometimes forget to add the carried-over ones back to the tens sum. Have them explain the calculation steps out loud.
How to practice at home
Do mental math in pairs, one solves it with jottings, the other checks.
Related: Number Sentences with a Gap, Written Addition, Semi-written multiplying