TITLE: Probability of picking 4 red balls
QUESTION [7 upvotes]: There are $6$ red balls and $5$ blue balls in a jar. You pick any $4$ balls without looking in  the jar. What is the probability that you would be having $4$ red balls in hand?

Note that you're picking up all the $4$ balls in one single attempt and not one-by-one. Also balls of same colour are to be considered as identical. 
I tried this and got the answer as $4/11$ which was wrong. I can't figure out what the cases (sample space) would be.

REPLY [11 votes]: The answer is easly given considering permutations. Indeed the probability is:
$$P =\frac{7!}{11!} \cdot \frac{6!}{2!}=\frac{1}{22}$$
where

$11$ is the total number of balls;
$7$ the number of balls remaining in the jar;
$6$ the number of red balls;
$2$ the number of red balls remaining in the jar.