find the sum of the number of combinations possible by using 12 , 34 such that no number is repeated ( ex : - 12234322 are invalid 12344321 are valid ) more than once .	Choose the correct choice from the following: A) 66660 B) 66760 C) 66860 D) 66960 E) 67660

Rationale: total no . formed = 4 ! = 4 * 3 * 2 * 1 = 24 each digit will be used at each positions , 6 times sum of digits at unit place = 6 * 1 + 6 * 2 + 6 * 3 + 6 * 4 = 6 * ( 1 + 2 + 3 + 4 ) = 60 this sum will be same for hundred , tens & unit places sum of all 4 digit numbers formed using digits 12 , 34 = 1000 * 60 + 100 * 60 + 10 * 60 + 60 = 60 * ( 1000 + 100 + 10 + 1 ) = 60 * 1111 = 66660 answer : a
Answer: A