Write all possible numbers using the digits 3, 1 and 5. Repetition of digits is not allowed.

We are required to write all possible numbers using the digits 3, 1 and 5, where repetition of digits is not allowed.

1-digit numbers: 1, 3, 5.

2-digit numbers:

Keeping 1 at unit's place: 31, 51.

Keeping 3 at unit's place: 13, 53.

Keeping 5 at unit's place: 15, 35.

2-digit numbers: 13, 15, 31, 35, 51, 53.

3-digit numbers:

Keeping 1 at unit's place: 351, 531.

Keeping 3 at unit's place: 153, 513.

Keeping 5 at unit's place: 135, 315.

3-digit numbers: 135, 153, 315, 351, 513, 531.

Hence, all possible numbers are: 1, 3, 5, 13, 15, 31, 35, 51, 53, 135, 153, 315, 351, 513 and 531.