16) Andrea did not do the homework exercises and as punishment, the teacher assigns him the task of writing in his notebook all the numbers between 1 and 2005, inclusive (each number must be written only once). How many digits will Andrea have to write in total?
(A) 6900,
(B) 6903
(C) 6910
(D) 6913,
(E) 6923.
16. The answer is (D). Between 1 and 2005 (inclusive) there are:

$$
\begin{aligned}
& \{1, \ldots, 9\}: 9 \text { numbers with one digit } \rightarrow 9 \times 1=9 \text { digits, } \\
& \{10, \ldots, 99\}: 90 \text { numbers with two digits } \rightarrow 90 \times 2=180 \text { digits, } \\
& \{100, \ldots, 999\}: 900 \text { numbers with three digits } \rightarrow 900 \times 3=2700 \text { digits, } \\
& \{1000, \ldots, 2005\}: 1006 \text { numbers with four digits } \rightarrow 1006 \times 4=4024 \text { digits. }
\end{aligned}
$$

The total number of digits is then: $9+180+2700+4024=6913$.