If p : q = r : s; then show that:

mp + nq : q = mr + ns : s

If p + r = mq and $\dfrac{1}{q} + \dfrac{1}{s} = \dfrac{m}{r};$ then prove that : p : q = r : s.

If a, b, c and d are in proportion, the value of $\dfrac{8a^2 - 5b^2}{8c^2 - 5d^2}$ is equal to :

1. a² : b²

2. a² : c²

3. a² : d²

4. c² : d²

$\dfrac{x + y}{z} = \dfrac{y + z}{x} = \dfrac{z + x}{y}$ is equal to :

1. 0

2. 1

3. 2

4. -2