3
5
6
2
9
7
8
1
4
6…8
,4…6
,9….11
10
,13….15,
14
17…….20.
1819
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13,14,15,16,17,18,19,20
7+8=
7+3
+5
=15
12-5=
12-2=10
-3=7
12-2-3=
Способ№1.
14-7=