一、口算。
$12 - 3 =$         $25 + 30 =$         $54 + 40 - 9 =$
$6 + 78 =$         $88 - 60 =$         $42 - 8 + 6 =$
$54 - 5 =$         $7 + 4 =$         $20 + 61 - 7 =$
$33 + 7 =$         $74 - 6 =$         $99 - 40 - 20 =$
$70 - 9 =$         $57 + 40 =$         $19 + 20 + 4 =$
$53 + 9 =$         $71 - 4 =$         $62 - 3 + 30 =$
$60 - 4 =$         $61 + 20 =$         $51 + 30 + 9 =$
$70 + 20 =$         $52 - 7 =$         $61 - 7 + 30 =$
$82 - 40 =$         $3 + 68 =$         $7 + 32 - 10 =$
$36 + 7 =$         $44 - 8 =$         $20 - 9 + 60 =$

一、9 55 85
84 28 40
49 11 74
40 68 39
61 97 43
62 67 89
56 81 90
90 45 84
42 71 29
43 36 71

二、先算一算，再将小鸟们按得数从大到小的顺序编号。
 

二、87 50
① ③
44 58
④ ②
19 5
⑤ ⑥