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smc

number theory senior

Problem

Let denote the sum of the even digits of . For example, . Find
(A)
(B)
(C)
(D)
Solution
The problem is asking for the sum of all the even digits in the numbers to . We can remove from the list, add to the list, and tack on some leading zeros to the single digit numbers without changing the sum of the even digits. This gives the list: . There are digits on that list, and each digit appears times. Thus, each even digit appears times, and the sum of all the even digits is , and the correct answer is .
Final answer
C