1.
Count backwards by 3s: 21, ___, 15, 12, 9, 6
2.
Count backwards by 3s: 21, 18, 15, ___, 9, 6
3.
Count backwards by 3s: 18, ___, 12, 9, 6, 3
4.
Count backwards by 2s: 10, 8, 6, 4, ___, 0
5.
Count backwards by 3s: 27, 24, ___, 18, 15, 12
6.
Count backwards by 3s: 27, 24, ___, 18, 15, 12
7.
Count backwards by 2s: 16, ___, 12, 10, 8, 6
8.
Count backwards by 2s: 10, 8, 6, ___, 2, 0
9.
Count backwards by 3s: 15, 12, ___, 6, 3, 0
10.
Count backwards by 3s: 24, 21, 18, ___, 12, 9
11.
Count backwards by 3s: 15, 12, 9, ___, 3, 0
12.
Count backwards by 2s: 12, 10, 8, ___, 4, 2
13.
Count backwards by 3s: 21, 18, ___, 12, 9, 6
14.
Count backwards by 3s: 27, ___, 21, 18, 15, 12
15.
Count backwards by 3s: 21, 18, 15, ___, 9, 6
16.
Count backwards by 3s: 21, 18, 15, 12, ___, 6
17.
Count backwards by 3s: 27, 24, 21, ___, 15, 12
18.
Count backwards by 2s: 14, ___, 10, 8, 6, 4
19.
Count backwards by 3s: 21, 18, 15, ___, 9, 6
20.
Count backwards by 3s: 15, 12, 9, 6, ___, 0