100
What comes before 13?
12
100
What comes after 16?
17
200
What comes before 17?
16
200
What comes after 21?
22
300
What comes before 22?
21
300
What comes after 11?
12
300
4, 6, 8, 10, _____
12
400
What comes before 1?
0
400
What comes after 9?
10
500
What comes before 20?
19
500
What comes after 29?
30