Thực hiện phép tính (tính hợp lý nếu có thể): a) 5.2^2-18:3; b) 85.18 + 18.16 - 18;

a) \[5 \cdot {2^2}-18:3\]

\[ = 5 \cdot 4-18:3\]

\[ = 20 - 6 = 14\]= 14.

b) \[85 \cdot 18 + 18 \cdot 16 - 18\]

\[ = 18 \cdot \left( {85 + 16 - 1} \right)\]

\[ = 18 \cdot 100 = 1800\]

c) \[{5^{20}}:\left( {{5^{15}} \cdot 6 + {5^{15}} \cdot 19} \right)\]

\[ = {5^{20}}:\left[ {{5^{15}} \cdot \left( {6 + 19} \right)} \right]\]

\[ = {5^{20}}:{5^{15}} \cdot \left( {6 + 19} \right)\]

\[ = {5^5}:25 = {5^3} = 125\].

d) \(720 - \left\{ {40 \cdot \left[ {\left( {120 - 70} \right):25 + {2^3}} \right]} \right\} + {2023^0}\)

\( = 720 - \left\{ {40 \cdot \left[ {{\rm{50}}:25 + {\rm{8}}} \right]} \right\} + 1\)\[ = 720 - \left\{ {40 \cdot \left[ {2 + {\rm{8}}} \right]} \right\} + 1\]

\[ = 720 - \left\{ {40 \cdot 10} \right\} + 1\]

\[ = 720 - 400 + 1 = 321\].