Question

(-1 - 2 - 3 - ... - 25):(-26) =
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Answer 1

 

$\displaystyle\bf\\(-1 - 2 - 3 - ... - 25):(-26)=\\\\-(1 + 2 + 3 + ... + 25):(-26)=\\\\=\frac{25\times26}{2}:26=\\\\=\frac{25\times26}{2}\times\frac{1}{26}=\frac{25\times26}{2\times26}=\boxed{\bf\frac{25}{2}}=\boxed{\bf12,5}$