A box contains 5 identical balls labeled $1$ to $5$. Drawing with replacement three times, let $X$ denote the number of distinct balls drawn at least once. Then the mathematical expectation $E(X) = $ $\_\_\_\_$ .
A box contains 5 identical balls labeled $1$ to $5$. Drawing with replacement three times, let $X$ denote the number of distinct balls drawn at least once. Then the mathematical expectation $E(X) = $ $\_\_\_\_$ .