Question: 2017 Winter Midterm - 17
Let $n \geq 1$ be an integer. A bag contains $n$ red balls and $n$ blue balls. We choose a uniformly
random subset of two balls. Define the event
- A = "this subset consists of one red ball and one blue ball".
(a)
$\left. {2n \choose 2} \middle/ n^2 \right.$
(b)
$\left. {n \choose 2} \middle/ n^2 \right.$
(c)
$\left. n^2 \middle/ {2n \choose 2} \right.$
(d)
$\left. n^2 \middle/ {n \choose 2} \right.$