This is a great mind trick but its all worked out mathematically like this..............

No matter what two-digit number you choose, once you do the little subtraction trick, you will end up with one of the following numbers: 9, 18, 27, 36, 45, 54, 63, 72, 81. And if you look at the grid closely, you will see that the same gift is in each of those numbered boxes.