14-7 6 18-9
13-7 5 12-6
15-7 7 11-6
12-3 9 16-9
13-8 8 17-9
3+8 14-10 2+4+5
11-7 5+6 15-6-1
16-9 13–5 12-9+4
14-6 14–7 10-6-0
写出3个十位上是7的两位数是:、、。
12-5=
47+247+20
78–578-50
>90>
57+4057-40
63+2053+30
+20<43