Probability of selecting three of the same thing from a collection Question: A collection of 6 items is to be randomly drawn from a bin containing 100 good items and 8 
defective items. What is the probability that exactly 3 of the items chosen are defective?
My Attempt: Well we know that in total there are 108 items. We know that you have a 8/108 chance of the first item being a defective one. I don't understand however, how we can figure out the other items, because it's dependent upon whether the first one was defective or not.
If anyone could explain this, I would greatly appreciate it.

Suppose all $8$ defective items belong in one set. If you want to choose $3$ defective items from this set, then you're looking for $3$-element subsets of this set. There are $\binom{8}{3}$ different $3$-element subsets of $8$-element set. If you follow this reasoning you get:
$$
\frac{\binom{8}{3}\binom{100}{3}}{\binom{108}{6}}
$$
Since you also need to select, $3$ good items from a $100$ and total of $6$ items from a $108$.
