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) - Insufficient. Lets plug in. X=5, Y=2. (5-2)*(5+2)=21, X=4, Y=2, (4+2)*(4-2)=12. Thus BCE. (2) Insufficient. Let plug in: X=1.3, Y=0.7. (1.3+0.7)*(1.3-0.7)=1.2 (X+Y is even, like is said in the statement). Thus CE
If taken together - Lets plug in X=3 Y=1 , (3+1)*(3-1)=8, X=4 Y=2, (4-2)*(4+2)=12. Sufficient!