If a, b, c and d are proportional, then $\dfrac{a + b}{a - b}$ is equal to:

1. $\dfrac{c}{d}$

2. $\dfrac{c-d}{c+d}$

3. $\dfrac{d}{c}$

4. $\dfrac{c+d}{c-d}$

Given,

a, b, c and d are proportional.

∴ a : b = c : d

$\Rightarrow \dfrac{a}{b} = \dfrac{c}{d}$

Applying componendo and dividendo, we get :

$\Rightarrow \dfrac{a + b}{a - b} = \dfrac{c + d}{c - d}$

Hence, option 4 is the correct option.