Number of problems

10 problems.
20 problems

Common difference

The difference can be positive: 3, 5, 7, 9, 11
The difference can be negative: 11, 9, 7, 5, 3

Blanks Location

Always give first 3 numbers: 3, 5, 7, _, _, _
Random, but always give 2 numbers next to each other: 3, _, _, 9, 11, _
Random, there may not be any numbers next to each other: 3, _, 7, _, _, 11, _

Answer sheet

Include answer sheet.