Learning to add quickly

With this program, you can work on adding and subtracting numbers into a column by selecting the correct numbers.
The program suggests putting the correct numbers in the empty cells. Select the cell and enter the number on the screen.
After filling in all the empty cells, check the result. After checking, you can see one of the correct answers by clicking the question mark button.
From the settings screen you can specify:
- number of digits for the first and second numbers;
- select the type of operation.