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smc

algebra senior

Problem

Let , and for integers . What is the sum of the digits of ?
(A)
(B)
(C)
(D)
Solution
Proof by induction that : For , Assume is true for n: Therefore, if it is true for n, then it is true for n+1; since it is also true for n = 1, it is true for all positive integers n. , which is the 2011-digit number 8888...8889 The sum of the digits is 8 times 2010 plus 9, or
Final answer
B