Oefen erbijsommen en erafsommen tot 20
In de mix
1.
20
0
+
=
2.
20
13
–
=
3.
13
6
+
=
4.
4
9
+
=
5.
18
0
+
=
6.
5
0
–
=
7.
17
8
–
=
8.
18
17
–
=
9.
3
3
–
=
10.
12
0
+
=
11.
9
1
–
=
12.
16
3
+
=
13.
16
14
–
=
14.
3
2
–
=
15.
14
13
–
=
16.
7
4
–
=
17.
19
15
–
=
18.
20
17
–
=
19.
12
5
+
=
20.
18
12
–
=
21.
20
0
+
=
22.
10
4
–
=
23.
14
6
+
=
24.
4
4
–
=