The four numbers in this 2-by-2 square add up to 20.
Search on the second grid.
Find five 2-by-2 squares where the four numbers add up to 20. Then find five squares with a total of 19.
Half and half
Take a 5 by 5 grid with the centre square cut out.
Divide it along the grid lines into two parts of the same size and shape.
In how many different ways can you do this?