In each square there are four numbers.
The numbers at the edge are the sums.
On the right is the sum for each row, at the bottom for each column.
Fill in the missing numbers so that all the sums are correct.
Example
What does this exercise practice?
This task trains flexible thinking with several conditions at once: children work out rows and columns and learn to find a number that meets both requirements.
Common pitfalls
Children often look only at the row or only at the column. Show that each box adds to both the row sum and the column sum, and have them check both after filling it in.
How to practice at home
Draw a 2x2 grid and fill three boxes with small numbers. The other person works out the fourth. Whoever names the correct number first gets to set the next puzzle.
Related: Wall, Magic square