Answer
$\displaystyle \frac{1}{2^{8}\cdot 5^{5}\cdot 5!}$
Work Step by Step
Number of ways to fill part A = $2^{8}$
( repeated choice of 1 out of two possibilities, 8 times)
Number of ways to fill part B = $5^{5}$
( repeated choice of 1 out of five possibilities, 5 times)
Number of arrangements for part C = $5!$
$n(S)=2^{8}\cdot 5^{5}\cdot 5!$
$ n(E)=1\qquad$ (the one way to have $100\%)$
$P(E)=\displaystyle \frac{1}{2^{8}\cdot 5^{5}\cdot 5!}$
