AMC 10 2015a Problem 18

Hexadecimal (base-16) numbers are written using numeric digits $0$ through $9$ as well as the letters $A$ through $F$ to represent $10$ through $15$. Among the first $1000$ positive integers, there are $n$ whose hexadecimal representation contains only numeric digits. What is the sum of the digits of $n$? $\textbf{(A) }17 \textbf{(B) }18 \textbf{(C) }19 \textbf{(D) }20 \textbf{(E) }21$