How many two-digit numbers have at least one digit that is a 4 ?
(A) 17
(B) 11
(C) 18
(D) 10
(E) 19
A two-digit number has at least one digit that is a 4 if its tens digit is a 4 or if its ones digit is a 4 .

There are 10 two-digit numbers whose tens digit is a 4.

These are $40,41,42,43,44,45,46,47,48$, and 49 .

There are 9 two-digit numbers whose ones digit is a 4 .

These are $14,24,34,44,54,64,74,84,94$, including 44 which was counted in our previous list. The number of two-digit numbers that have at least one digit that is a 4 is $10+9-1=18$.

ANSWER: (C)