8 + 2 = 10
7 + 3 = 10
6 + 4 = 10
9 + 1 = 10
5 + 5 = 10
 
10 − 4 = 6
14 − 4 = 10
8 − 4 = 4
9 − 4 = 5
4 − 4 = 0