Question \( 1-10 \) Which expression is equivalent to \( 2.5^{2-3 y} \) ? \( \begin{array}{l}\frac{6.25}{(15.625)^{-y}} \\ 6.25(2.5)^{3 y} \\ 6.25-(2.5)^{3 y} \\ 6.25(15.625)^{-y}\end{array} \)

To simplify \( 2.5^{2-3y} \), we can break it into two parts: \( 2.5^{2} \) and \( 2.5^{-3y} \). Since \( 2.5^{2} = 6.25 \) and \( 2.5^{-3y} = \frac{1}{2.5^{3y}} \), we can rewrite the expression as \( 6.25 \cdot 2.5^{-3y} \). Recognizing that \( 2.5^{-3y} \) can be expressed as \( \frac{1}{15.625^y} \) (since \( 15.625 = 2.5^4 \)) helps us express it in various forms. As a result, it leads us to identify that \( 6.25(15.625)^{-y} \) is equivalent to the original expression. So, the correct expression that is equivalent to \( 2.5^{2-3y} \) is: \( 6.25(15.625)^{-y} \).