If all the numbers between 11 and 100 are written on a piece of paper. How many times will the number 4 be used?  Pick:
A) 87 B) 267 C) 68 D) 26 E) 21

Rationale: we have to consider the number of 4 ' s in two digit numbers . _ _ if we fix 4 in the 10 th place , unit place be filled with 10 ways . if we fix 4 in units place , 10 th place be filled with 9 ways ( 0 is not allowed ) so total 19 ways . alternatively : answer : a
Answer: A