You should just add the numbers to 100. The row sums and columns sums should be 100. This wonderful number game trains your brain and also provides good entertainment.
There are timed games for those of you who like a challenge. If you feel adding to 100 is too easy, in level 8 and higher, the sum will be different each time. In more advanced levels, sum will be 1000.
Even children can play this game and hone their skills. Or even beat you :)
Have infinite fun!!!