One card is face down, find the missing number!
The number shown gives the answer.
Example
For parents
What does this exercise practice?
This task trains reverse thinking in addition: children learn to work out the missing number starting from the known sum, a core skill for later equations.
Common pitfalls
Children add all the visible cards but forget that the sum is already given. Show the structure: known numbers + ? = sum, so ? = sum minus the known numbers.
How to practice at home
Lay a few coins on the table and cover one. How many coins are hidden? You know the sum and you count the visible ones. Everyone gets a turn to hide the coin.
Related: Calculation, Inverse