\[\boxed{\text{1200.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[\textbf{а)}\ 5^{m} \cdot 5^{m + 1} \cdot 5^{1 - m} =\]
\[= 5^{m + m + 1 + 1 - m} = 5^{m + 2}\]
\[\textbf{б)}\ \left( 5^{m} \right)^{2} \cdot \left( 5^{- 3} \right)^{m} =\]
\[= 5^{2m} \cdot 5^{- 3m} =\]
\[= 5^{2m + ( - 3m)} = 5^{- m}\]
\[\textbf{в)}\ 625\ :5^{4m - 2} = 5^{4}\ :5^{4m - 2} =\]
\[= 5^{4 - 4m + 2} = 5^{6 - 4m}\]