If a/b = 1/2, find the value of the expression ( 2a - 5b ) ( 5a + 3b ) = ?

Answer: Option C

$$\begin{array}{rl}& \frac{a}{b}=\frac{1}{2}\\ & \text{Let }a=x,b=2x\\ & \text{Then,}\frac{\left(2a-5b\right)}{\left(5a+3b\right)}\\ & =\frac{2x-10x}{5x+6x}\\ & \text{ = }\frac{-8x}{11x}\\ & =\frac{-8}{11}\end{array}$$