Here a number puzzle that can be made as easy or as difficult as you wish.
You only need a piece of paper and a pen.
On a piece of paper draw five boxes so they from an 'L' shape, like this:

Now, can you put the numbers 0, 1, 2, 3 and 4 in the boxes so that the total going down the 'L' is the same as the total going across?
Try it for yourself before looking at this solution
There's more than one way of doing this. Draw more 'L' shapes and see if you can find another way.
Can you find eight different ways?
What do you notice?
Next, try it with different numbers.
What happens if you use these numbers:
0, 3, 6, 9, 12
7, 8, 9, 10, 11
5, 9, 13, 17, 21
Choose some of your own numbers.
Finally, try it with a larger 'L' shape. Can you make one with 4 squares on each side?
What numbers would you choose to write in this new puzzle?
How many different ways can you place the numbers in this puzzle?