2013 UNCO Math Contest II Problems/Problem 8

Revision as of 18:23, 19 October 2014 by Timneh (talk | contribs) (moved 2013 UNC Math Contest II Problems/Problem 8 to 2013 UNCO Math Contest II Problems/Problem 8: disambiguation of University of Northern Colorado with University of North Carolina)

Problem

EXAMPLE: The non-terminating periodic decimal $0.124124 \ldots = 0.\overline{124}$ has period three and is abbreviated by placing a bar over the shortest repeating block.

(a) If all digits $0$ through $9$ are allowed, how many distinct periodic decimals $0.\overline{d_1d_2 \ldots d_6}$ have period exactly six? Do not include patterns like $0.323$ and $0.17$ that have shorter periods.

(b) If only digits $0$ and $1$ are allowed, how many distinct periodic decimals $0.\overline{d_1d_2\ldots d_{12}}$ have period exactly $12$?


Solution

See Also