Write the greatest 4-digit number that can be formed by the digits 0, 2, 7 and 5, using each digit only once.

The given digits are: 0, 2, 7, 5.

Arranging them in descending order:

Largest digit: 7 (for the thousands place)

Next largest: 5 (for the hundreds place)

Next largest: 2 (for the tens place)

Smallest digit: 0 (for the units place)

Hence, the greatest 4-digit number that can be formed is 7520.