Thực hiện phép tính (tính hợp lí nếu có thể):

a) \[245:\left( {{8^2}-15} \right)\]

\( = 245:\left( {64 - 15} \right)\)

\( = 245:49\)

\( = 5\).

b) \(215 + 43 + \left( { - 215} \right) + \left( { - 25} \right)\)

\( = \left[ {215 + \left( { - 215} \right)} \right] + 43 + \left( { - 25} \right)\)

\( = 43 - 25\)

\( = 18\).

c) \(\left( { - 16} \right).25.\left( { - 125} \right).\left( { - 12} \right)\)

\( = \left( { - 8} \right).2.25.\left( { - 125} \right).\left( { - 6} \right).2\)

\[ = \left[ {\left( { - 8} \right).\left( { - 125} \right)} \right].\left( {2.25.2} \right).\left( { - 6} \right)\]

\[ = 1000.100.\left( { - 6} \right)\]

\( =  - 600\,\,000\).

d) \(53.89 + {6^2}.53 - {53.5^2}\)

\( = 53.\left( {89 + {6^2} - {5^2}} \right)\)

\( = 53.\left( {89 + 36 - 25} \right)\)

\( = 53.100\)

\( = 5\,\,300\).