Answer
$-\frac{39}{40}$
Work Step by Step
$-\frac{1}{10}-\frac{7}{8}=-\frac{1\times4}{10\times4}-\frac{7\times5}{8\times}=-\frac{4}{40}-\frac{35}{40}=\frac{-4-35}{40}=\frac{-4+(-35)}{40}=\frac{-39}{40}=-\frac{39}{40}$
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