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we can do this if we can find out 2 things:
1) The number of 4-digit numbers where none of the digits are the same.
2) The total number of 4-digits numbers that we can form with the given numbers.

Using the numbers 1, 3, 5, 7 and 9, there are x 4-digit numbers, in which at least 2 digits are the same. Therefore, x must be:

(A) 505 (B) 427 (C) 120 (D) 625 (E) 384

There are 5 possible numbers.
Number of all possible 4 digit numbers = 5^4 = 625
Number of 4 digit numbers with distinct numbers = 5.4.3.2 = 120
Hence answer is 625 - 120 = 505