If y = 5 , then what is the value of 10y y^3 - y^2 = ?

Answer: Option D

$$\begin{array}{rl}& =10y\sqrt{y^3-y^2}\\ & =10\times 5\sqrt{5^3-5^2}\\ & =50\times \sqrt{125-25}\\ & =50\times \sqrt{100}\\ & =50\times 10\\ & =500\end{array}$$