If n is a positive integer, write s(n) for the sum of the digits of n. What is
s(1) + s(2) + s(3) +...+ s(1000)?  Select the correct option.
A) 9991  B) 10000  C) 13501  D) 14999  E) 15000
We start by computing S := s(0) + s(1) + s(2) + s(3) + ...+ s(999). Each digit,   0 through 9, appears equally often: 100 times in the hundreds place, 100 times in the tens   place, and 100 times in the ones place. (Here we write, e.g., 3 as 003.) Therefore,   S = 300* 0 + 300 * 1 + + 300 * 9 = 300(0 + 1 +...+ 9) = 300 *45= 
<gadget id="calculator">300 *45</gadget>
<output>13_500</output>
13500:   Since s(0)= 0 and s(1000) = 1 we obtain the answer.   correct answer 13501
<result>C</result>
If n is a positive integer, write s(n) for the sum of the digits of n. What is
s(1) + s(2) + s(3) +...+ s(1000)?