find how many 4 digits no. is less then 1239 such that all 4 digits are distinct.  Choices:
A) 68
B) 69
C) 70
D) 71
E) 72

Rationale: case 1 - 1000 - 1099 - there are 56 distinct digits case 2 - 1200 - 1209 - there are 7 distinct digits case 3 - 1230 - 1239 ( excluding 1239 ) - there are 6 distinct digits hence , 56 + 7 + 6 = 69 answer : b
Answer: B