Đáp án:
$\begin{array}{l}
a)215 + \left( { - 38} \right) - \left( { - 58} \right) + 90 - 85\\
= \left( {215 - 85} \right) + \left( { - 38 + 58} \right) + 90\\
= 130 + \left( {58 - 38} \right) + 90\\
= 130 + 20 + 90\\
= 240\\
b)31 - \left[ {26 - \left( {209 + 35} \right)} \right]\\
= 31 - \left( {26 - 209 - 35} \right)\\
= 31 - 26 + 209 + 35\\
= \left( {31 + 209} \right) + \left( {35 - 26} \right)\\
= 240 - 9\\
= 231\\
c)314 - \left( {41 + 204} \right)\\
= 314 - 41 - 204\\
= \left( {314 - 204} \right) - 41\\
= 110 - 41\\
= 69\\
d)917 - \left( {417 - 65} \right)\\
= 917 - 417 + 65\\
= 500 + 65\\
= 565
\end{array}$
