一、口算。
$□ + 7 = 17$
$7 + 8 =$
$14 - 7 + 6 =$
$8 + □ = 14$
$16 - 8 =$
$8 + 5 - 7 =$
$□ + 7 = 12$
$11 - 7 =$
$12 - 7 + 5 =$
$8 + □ = 13$
$11 - 8 =$
$17 - 8 - 7 =$
$7 + □ = 11$
$7 + 6 =$
$7 + 6 - 8 =$
$8 + □ = 12$
$15 - 7 =$
$11 - 7 + 15 =$
$7 + □ = 13$
$16 - 8 =$
$13 - 2 - 7 =$
$8 + □ = 15$
$7 + 7 =$
$16 - 9 + 4 =$
$□ + 7 = 16$
$13 - 8 =$
$7 + 4 - 8 =$
$□ + 8 = 17$
$12 - 7 =$
$13 - 7 + 10 =$

一、10 15 13
6 8 6
5 4 10
5 3 2
4 13 5
4 8 19
6 8 4
7 14 11
9 5 3
9 5 16

二、每次选三张卡片，组成三道得数是 9 的减法算式。

二、18−9 17−8
16−7