7先圈一圈，再计算
$24 - 9 = □$
先算 $14 - 9 = □$
再算 $□ + □ = □$
$40 - 6 = □$
先算 $10 - □ = □$

再算 $□ + □ = □$
$□ ◯ □ = □$
先算 $□ - □ = □$
再算 $□ + □ = □$

$24 - 9 = 15$
先算 $14 - 9 = 5$
再算 $10 + 5 = 15$
$40 - 6 = 34$
先算 $10 - 6 = 4$
再算 $30 + 4 = 34$
$33 - 4 = 29$
先算 $13 - 4 = 9$
再算 $20 + 9 = 29$

算一算
$23 - 5 =$
$51 - 9 =$
$35 - 7 =$
$92 - 5 =$
$20 - 7 =$
$52 - 3 =$
$73 - 9 =$
$38 - 9 =$
$66 - 8 =$
$36 - 7 =$
$53 - 4 =$
$80 - 6 =$
$32 - 7 =$
$42 - 3 =$
$90 - 9 =$
$51 - 2 =$
$62 - 7 =$

23-5=18
51-9=42
35-7=28
92-5=87
20-7=13
52-3=49
73-9=64
38-9=29
66-8=58
36-7=29
53-4=49
80-6=74
32-7=25
42-3=39
90-9=81
51-2=49
62-7=55