Over a six$-$year period, the returns to the S&P $500$ Index were: $23\mathrm{.}5\%,12\mathrm{.}8\%,0\mathrm{.}0\%,13\mathrm{.}4\%,29\mathrm{.}6\%,11\mathrm{.}4\%.$ Compute the arithmetic average annual return for the S&P $500$ Index for this time period.

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