If 8a = 9b, then the ratio of $\dfrac{a}{9}$ to $\dfrac{b}{8}$ is:

1. 1 : 1

2. 1 : 2

3. 2 : 1

4. 64 : 81

Given,

8a = 9b

$\therefore \dfrac{a}{b} = \dfrac{9}{8}$

Solving,

$\Rightarrow \dfrac{\dfrac{a}{9}}{\dfrac{b}{8}} \\[1em] \Rightarrow \dfrac{a}{9} \times \dfrac{8}{b} \\[1em] \Rightarrow \dfrac{8a}{9b} \\[1em] \Rightarrow \dfrac{8}{9} \times \dfrac{9}{8} \\[1em] \Rightarrow \dfrac{9}{9} \\[1em] \Rightarrow \dfrac{1}{1} \\[1em] \Rightarrow 1 : 1.$

Hence, option 1 is the correct option.