一、在$□$里填合适的数。
$9 + 7 = □$
$9 + 9 = □$
$9 + 8 = □$

一、9+7=16

9+9=18

9+8=17

二、口算。
$9 + 1 + 1 =$
$9 + 1 + 2 =$
$9 + 1 + 3 =$
$9 + 2 =$
$9 + 3 =$
$9 + 4 =$
$9 + 1 + 4 =$
$9 + 1 + 5 =$
$9 + 1 + 6 =$
$9 + 5 =$
$9 + 6 =$
$9 + 7 =$
$9 + 1 + 7 =$
$9 + 1 + 8 =$
$9 + 1 + 9 =$
$9 + 8 =$
$9 + 9 =$
$9 + 10 =$
$9 + 2 - 1 =$
$10 - 1 + 5 =$
$9 + 5 - 4 =$
$8 + 1 + 7 =$
$3 + 6 + 8 =$
$4 + 5 + 9 =$
$5 + 4 + 10 =$
$2 + 7 + 7 =$
$9 + 9 - 8 =$
$9 + 7 - 3 =$
$9 + 5 - 2 =$
$9 + 6 + 4 =$

二、11 12 13
11 12 13
14 15 16
14 15 16
17 18 19
17 18 19
10 14 10
16 17 18
19 16 10
13 12 19