A number is missing in every task. It is hiding in the empty box.
Sometimes the result is missing, sometimes one of the two numbers.
Example: 4234 + 3123 = box, so 7357.
Example: Box − 21345 = 54321. Work backwards: 54321 + 21345 = 75666.
The numbers written in show the answer.
Example
4234+3123=7357
75666−21345=54321
For parents
What does this exercise practice?
Solving plus and minus tasks with big numbers in your head, even when the gap is in different places.
Common pitfalls
If the gap is at the front, many children simply calculate away. The question helps: which sum leads back to the given number? With big numbers it helps to calculate with the thousands first and then add the remaining places.
How to practice at home
Think up a task with a gap, for example 340000 plus how much makes 560000?
Related: Mental Math with Jottings, Written Addition, Column subtraction