# Binomial or Geometric distribution?

• Feb 3rd 2011, 05:34 PM
Trill
Binomial or Geometric distribution?
Can someone please help me out with this. I've been trying for about forty minutes, but I'm not getting this. Trust me, I've done everything I can to try to look up strategies/tips on these types of problems, but it's not helping. I REALLY appreciate any assistance! :)

32% of employed women have never been married. Suppose you randomly select 10 employed women and determine marital history.

1) What is the random var X of interest here? Define X. Is X binomial, geometric, or normal?
2) If 10 employed women are selected at random, what is the prb that 2 or fewer have never been married?
3) What are the mean and standard deviation of X?
4) Find the prb that the # of employed women who have never been married is within 1 standard deviation of its mean.

70% of Americans are overweight. Suppose that a # randomly selected are weighed.

5) Find the prb that 18 or more of the 30 students in a class are overweight
6) How many Americans would you expect to weigh before you encounter the first overweight individual?
7) What is the prb that it takes more than 5 attempts before an overweight person is found?

Thank you so so so so much if you could help! I really appreciate it!
• Feb 3rd 2011, 05:46 PM
harish21
a binomial RV.. can you do 2,3 and 4?
• Feb 3rd 2011, 06:09 PM
Trill
I'm sorry, I'm really having trouble with this concept. For the first group of problems, I got that it's binomial.

p = 0.32 -- Never married
q = 1 - 0.32 = 0.68 = -- Married
n = 10

I just don't really know what to do from there (and defining X?).

The second group of problems is even worse for me.
• Feb 3rd 2011, 06:26 PM
harish21
You should read from your notes what binomial distribution is and how it is used.

1) X is binomial

2) $p = 0.32 \;\;\; 1 = 0.68\;\;\;n=10$

for a binomial $P(X=x) = \dbinom{n}{x} p^x (1-p)^{n-x}$. Using this, find

$P(X \leq 2) = P(X=0)+P(X=1)+P(X=2)$

3) mean and sd should be in you book.. its just plugging values of n and p into the formula of n and p..

I suggest you to look at your notes or read about Binomial Distribution to get a proper grasp.