Đáp án:
$\begin{array}{l}
a)17.\left( {15 - 16} \right) + 16.\left( {17 - 20} \right)\\
= 17.15 - 17.16 + 16.17 - 16.20\\
= 17.15 - 16.20\\
= 16.15 + 15 - 16.20\\
= 16.\left( {15 - 20} \right) + 15\\
= 16.\left( { - 5} \right) + 15\\
= 5\left( { - 16 + 3} \right)\\
= 5.\left( { - 13} \right)\\
= - 65\\
b)23.\left( {145 - 17} \right) - 145.\left( {23 - 6} \right)\\
= 23.145 - 23.17 - 145.23 + 145.6\\
= 145.6 - 23.17\\
= 479\\
c) - 38.\left( {25 - 4} \right) + 25.\left( { - 4 + 38} \right)\\
= - 38.25 + 38.4 - 25.4 + 25.38\\
= \left( {38 - 25} \right).4\\
= 13.4\\
= 52\\
d)24\left( {15 - 4} \right) + 4\left( {24 - 15} \right)\\
= 24.4 - 4.15\\
= 4.\left( {24 - 15} \right)\\
= 4.9\\
= 36\\
e) - 39\left( {5 - 99} \right) + 99\left( {10 - 39} \right)\\
= - 39.5 + 99.10\\
= 5.\left( { - 39 + 99.2} \right)\\
= 5.159\\
= 795
\end{array}$
