### Instruction:
Classify each of the following as either a single digit or a double digit number: 8, 4, 1, 12, 87, 65, 3, 5, 45, 97, 6, 2, 34, 71, 9, 48, 0, 7, 31, 50.

### Response:
Single digits include: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
Double digits include: 12, 31, 34, 45, 48, 50, 65, 71, 87, 97.