[Euler-Fermat]

14.$n(S) = 3^5$

$n(E) = \dfrac{5!}{2!2!} = 30$

$P(E) = a = \dfrac{30}{243} $

$\therefore \dfrac{10}{a} = 81$

20.$n(S) = 3^{12}$

$n(E) = 3^{12} - (8*3^{10})$

$P(E) = P = \dfrac{3^{12}-(8*3^{10})}{3^{12}} = \dfrac{3^{10}}{3^{12}} = \dfrac{1}{9}$

$\therefore 144P = 144*\dfrac{1}{9} = 16$