The house number is in the roof. On every floor two numbers live that together make the house number.
Example: the roof shows 63.
One floor already has the 21. Which number is missing?
21 + 42 = 63, so the 42 belongs next to it.
Tip: count up from the number you know to the house number.
The numbers filled in show the solution.
Example
For parents
What does this exercise practice?
Find the splits of a number confidently and practice completing up to a target number.
Common pitfalls
Some children add the two numbers instead of completing. Ask: how far is it from this number up to the roof?
How to practice at home
Build the house number with blocks. Split it into two piles and check whether both together give the house number again.
Related: Break apart, Calculation, Inverse