2DigitSubtractionByWriting

At first I Made a multiplication exercises app, but for computation by writing at the two-digit subtraction, my son has so many problems. So I made an app that can practice the calculation by writing of the subtraction.
There are two parts subtraction and subtraction carry, and provided the practice of 150 set. There is 20 die in one set, one set one day.
I think it provides a set portion of the 100 have carry in particular, to be able to practice carefully.
There is also an alarm and statistics function.