450 views
2 votes
A bag contains 20 white marbles and 30 black marbles. if 7 marbles are chosen, what is the probability that there will be 2 white marbles and 5 black marbles?

User Bmitc
by
8.2k points

1 Answer

1 vote
This is a hypergeometric distribution problem.
Population (N=50=W+B) is divided into two classes, W (W=20) and B (B=30).
We calculate the probability of choosing w (w=2) white and b (b=5) black marbles.
Hypergeometric probability gives
P(W,B,w,b)=C(W,w)C(B,b)/(C(W+B,w+b)
where
C(n,r)=n!/(r!(n-r)!) the number of combinations of choosing r out of n objects.

Here
P(20,30,2,5)
=C(20,2)C(30,5)/(20+30, 2+5)
=190*142506/99884400
=0.2710

Alternatively, doing the combinatorics way:
#of ways to choose 2 from 20 =C(20,2)
#of ways to choose 5 from 30=C(30,5)
total #of ways = C(50,7)
P(20,30,2,5)=C(20,2)*C(30,5)/C(50,7)
=0.2710
as before.
User Kusi
by
8.1k points

No related questions found

Welcome to QAmmunity.org, where you can ask questions and receive answers from other members of our community.

9.4m questions

12.2m answers

Categories