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