Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
1) Z=12 so XY=12 sufficient
2) X+Y+Z=20 sufficient because say Z is the largest number, so Z=20 - Y -X
therefore it must be that XY=20 - Y - X, it works for X and Y being equal to 2 or 6
so XY=12 and no others