# Thread: probability >>>> my solution truth or not??

1. ## probability >>>> my solution truth or not??

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

2. Originally Posted by flower3
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 Mr F says: Correct.

(2)
mean = 88\20 Mr F says: Correct.
And you realise that the number of successful balls drawn follows a hypergeometric distribution?

3. And you realise that the number of successful balls drawn follows a hypergeometric distribution?
yes i know that because i use the law of mean for 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