Form the smallest and greatest 4-digit numbers by using any one digit twice from the digits:

(i) 5, 2, 3, 9

(ii) 6, 0, 1, 4

(iii) 4, 6, 1, 5, 8

(i) The given digits are 5, 2, 3 and 9.

For the greatest 4-digit number, use the largest digit twice. So, use 9 twice. The next largest digits are 5 and 3.

Arrange in descending order: 9, 9, 5, 3.

The greatest 4-digit number = 9,953.

For the smallest 4-digit number, use the smallest digit twice. So, use 2 twice. The other two smaller digits are 3 and 5.

Arrange in ascending order: 2, 2, 3, 5.

The smallest 4-digit number = 2,235.

Hence, the greatest 4-digit number is 9,953 and the smallest 4-digit number is 2,235.

(ii) The given digits are 6, 0, 1 and 4.

For the greatest 4-digit number, use the largest digit twice. So, use 6 twice. The next largest digits are 4 and 1.

Arrange in descending order: 6, 6, 4, 1.

The greatest 4-digit number = 6,641.

For the smallest 4-digit number, use the smallest digit twice. So, use 0 twice. The other two smaller digits are 1 and 4.

Since 0 cannot be at the thousand's place, the next smallest non-zero digit (1) is placed at the thousand's place, then 0, 0, 4 in order.

The smallest 4-digit number = 1,004.

Hence, the greatest 4-digit number is 6,641 and the smallest 4-digit number is 1,004.

(iii) The given digits are 4, 6, 1, 5 and 8.

For the greatest 4-digit number, use the largest digit twice. So, use 8 twice. The next largest digits from the remaining are 6 and 5.

Arrange in descending order: 8, 8, 6, 5.

The greatest 4-digit number = 8,865.

For the smallest 4-digit number, use the smallest digit twice. So, use 1 twice. The other two smaller digits from the remaining are 4 and 5.

Arrange in ascending order: 1, 1, 4, 5.

The smallest 4-digit number = 1,145.

Hence, the greatest 4-digit number is 8,865 and the smallest 4-digit number is 1,145.