Number Waterfall - Add Games

Simulate a waterfall using numbers. Waterfall is considered well-formed only if: - Sum of the numbers is equal to the goal. - Marked numbers should be adjacent horizontal, vertical & diagonally. That is, no empty line union. - 2 numbers marked on each row. Also available a challenges section, where different variations appear. In both cases, there are two levels: normal & difficult. In the normal level, the sum is shown, however, in the difficult level, you will have to add & subtract mentally b...