What is the sum of all 3 digit positive integers that can be formed using the digits 1, 3, and 6, if the digits are allowed to repeat within a number? Choose the correct choice from the following answers.
A) 6660  B) 7770  C) 8880  D) 9990  E) 10,110
The number of these 3-digit numbers is   3*3*3= 
<gadget id="calculator">  3*3*3</gadget>
<output>27</output>
27   Each digit 1, 3, and 6 will appear in the ones, tens, and hundreds place 9 times each.   The sum equals 9(111) + 9(333) + 9(666)= 9,990   The answer is 9990.
<result>D</result>
What is the sum of all 3 digit positive integers that can be formed using the digits 1, 3, and 6, if the digits are allowed to repeat within a number?