Using the digits 3, 8, 0, 5 form:

(a) The greatest 4-digit number (without repeating any digit)

(b) The smallest 4-digit number (without repeating any digit)

(a) To form the greatest number, arrange the digits in descending order:

8 > 5 > 3 > 0, so the greatest 4-digit number = 8530.

(b) To form the smallest number, arrange the digits in ascending order. The thousands place cannot be 0, so we place the smallest non-zero digit (3) first:

Smallest 4-digit number = 3058.