how many 4 - digit odd numbers do not use any digit more than once ?
Choose the correct choice from the following options:
A) 1728
B) 2160
C) 2240
D) 2268
E) 2520

Rationale: let a 4 - digit number be represented by abcd here a can have any value between 1 to 9 - so total 9 b can have any value between 0 to 9 , but not a - so total 9 c can have any value between 0 to 9 , but not a or b - so total 8 d can have any value between 0 to 9 , but not a , b or c - so total 7 no . of all possible 4 - digit nos ( without repeating any digit ) = 9 * 9 * 8 * 7 = 4536 half of these would be odd . therefor , no . of odd possible 4 - digit nos ( without repeating any digit ) = 4536 / 2 = 2268 answer should be d .
Answer: D