a box contain :
7white
3red
4black
and 6 green balls
if we choose 8 balls randomly without replacement . if selecting a white or a black ball is consider as wining >>>find :
(1) the probability that we get 6 wining balls
(2) the expected value for number of wining
my solutions:
(1)f(x)=
(11C6)*(9C2)\(20C8)
C: means combination
(2)
mean = 88\20
yes i know that because i use the law of mean for a hypergeometric distribution :And you realise that the number of successful balls drawn follows a hypergeometric distribution?
mu = nr\N
n:#of balls drawn
r: # of total success=the balls that make us wining
N: # of total balls
mu = nr\N
=(11*8) \ 20