How many different three-digit integers have exactly three different digits?
(A) 504
(B) 648
(C) 720
(D) 891
(E) 1,000
(A) 504
(B) 648
(C) 720
(D) 891
(E) 1,000
Question asks how many 3 digit numbers can be formed without repetition.
10 integers 0-9
0 cannot be at hundreds place so 1st place 9
0 can be at tens place, total 10, reject 1 from 1st place = 9
0 can be at tens place, total 10, reject 2 from 1st and 2nd = 8
Total ways = 9*9*8 = 648
