Math Help - Discrete probobility distributions

1. Discrete probobility distributions

Okay, so my book is horrible and it doesnt explain things very well and i cant seem to find my answer anywhere online.

I wont write out the example in the book since i think its irrelevant and way to long. I am struggling with the notation and how they get the answer.

$f(0) = P(X=0) = \frac{\left[\begin{array}{cc}3 \\0 \\\end{array}\right] \left[\begin{array}{cc}17 \\2 \\\end{array}\right]}{\left[\begin{array}{cc}20 \\2 \\\end{array}\right]} = \frac{68}{95}$

I m very confused on how they got the answer.
I think the (3 0 ) = 0?

Can someone please explain and
work this out because i am completely lost and i am sure its easy.
I am wiling to look at a webpage if i knew what to look up.

Thank you

2. Re: Discrete probobility distributions

Hey icelated.

Hint: 3C0 is not 0: it's 1 since 3!/(0!*3!) = 1.