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1999 AHSME Problems/Problem 3

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To find the number halfway between \frac{1}{8} and \frac{1}{10}, simply take the arithmetic mean, which is

\frac{\frac{1}{8}+\frac{1}{10}}{2}=\frac{\frac{9}{40}}{2}=\frac{9}{80}.

Thus the answer is choice \boxed{E}.

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