1. 算一算。

11 – 3 =           11 – 5 =        11 – 9 =       11 – 10 =

11 – 6 =           5 +6 =          4 +8 =         7 +9 =

11 – 4 =           11 – 2 =         7 +5 =         3 + 9 =