Let A = \ 2, 3, 4, 5, . , 30\ and ' ≃ ' be an equivalence relation...

A = \left\{2, 3, 4, 5, \ldots , , 30\right\}$</p><p>\left(a, b\right) = \left(c, d\right) ⇒ ad = bc$

\left(4, 3\right) = \left(c, d\right) ⇒ 4d = 3c$</p><p>$⇒ \dfrac{4}{3} = \dfrac{c}{d}$</p><p>$\dfrac{c}{d} = \dfrac{4}{3} \text{ and } c, d \in \left\{2, 3, \ldots \ldots , 30\right\}$</p><p>\left(c, d\right) = \left\{\left(4, 3\right), \left(8, 6\right), \left(12, 9\right), \left(16, 12\right), \left(20, 15\right), \left(24, 18\right), \left(28, 21\right)\right\}$

No. of ordered pair $= 7$