One card is face down, find the missing number!
Later there is a minus in between: then the missing number is the one taken away.
The number shown gives the answer.
Example
For parents
What does this exercise practice?
This task trains reverse thinking in arithmetic: children learn to work out the missing number starting from the known result, first in addition and later in subtraction, a core skill for later equations.
Common pitfalls
Children add all the visible cards but forget that the result is already given. Show the structure: known number + ? = result, so ? = result minus the known number. With minus it is the other way around: 9 − ? = 4 means 5 was taken away.
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: Math Problems with a Gap, Inverse Problems