Final answer:
A total of 900 4-digit numbers can be formed if repetitions are not allowed and the numbers always end with 3.
Step-by-step explanation:
The number of 4-digit numbers that can be formed if repetitions are not allowed and the numbers always end with 3 can be determined using permutations. T
here are 9 choices for the first digit (0-9 except 3), 10 choices for the second digit (0-9), 10 choices for the third digit (0-9), and only 1 choice for the last digit (3).
Therefore, the total number of 4-digit numbers is 9 * 10 * 10 * 1 = 900.