Answer
12
Work Step by Step
The probability of drawing a club from a deck of cards is $p=\frac{13}{52}=0.25$,
let $k=3$ be the number of successes, based on the negative binomial distribution formula,
we have $\mu=\frac{k}{p}=\frac{3}{0.25}=12$
Thus, the average number of trials needed to get 3 clubs is $12$.
