口算.
9 + 3 = 8 + 4 = 7 + 7 = 18 - 6 =
7 + 8 = 9 + 4 = 17 - 4 = 16 - 5 =
7 + 9 = 6 + 7 = 6 + 6 = 10 + 6 =
( )+ 7 = 12 6 +( )= 17 ( )+ 5 = 7 + 4
( )- 4 = 10 14 -( )= 11 ( )- 5 = 2 + 9
3 + 5 + 6 = 6 + 4 + 8 = 6 + 9 + 3 =
18 - 8 + 3 = 7 + 6 - 3 = 17 - 5 + 4 =