Probability question help

anonimnystefy · 2012-03-02 06:23:41

hi bob

i'm sorry to interfere,i just want to point out another way of computing that probability.

hi finitehelp

notice that the probability that at most one woman is picked would be the opposite of two women being picked.so we can differently calculate P(at least one woman)=1-P(two women being picked. )

Bob · 2012-03-02 06:25:27

Correct! well done.

Now you may cancel down.

OK let's move on to the mean of the distribution.

This is sometimes also called the expected value.

So if you choose two representatives over and over again and again, at random, and asked what is (total females chosen)/(total number of times you did this) this would be the average number of females per group.

It may not be a whole number.

the formula is

Bob

Bob · 2012-03-02 06:27:31

hi Stefy,

Sure you can. I was trying to make each calculation like the previous one so finitehelp learns to work consistently with no short cuts.

And your way gives 1 - 2/30 = 28/30 That's fine as a method too.

Bob

finitehelp · 2012-03-02 06:35:34

(x x p(x))=2/3 now im stuck here

Bob · 2012-03-02 06:38:49

That's correct.

what are you stuck on?

the standard deviation?

Bob

finitehelp · 2012-03-02 06:39:50

yup

Bob · 2012-03-02 06:52:30

OK.

The mean is the expected value.

The standard deviation is a measure of how spread out the possible Xs are.

There are two different fomrulas for the sd,

(i)

(ii)

i don't know why i'm getting two )) here.

Do either of these look familiar?

Bob

Bob · 2012-03-02 06:57:30

I have it now.

(ii)

Bob

anonimnystefy · 2012-03-02 07:13:04

LaTeXing problems?

Bob · 2012-03-02 07:21:46

All the time.

But actually, this was just me being stupid. I'd actually typed two open and two close brackets. It just happened that the two )) came together.

I solved the problem by getting rid of one set completely. The meaning of the formula is still clear I think.

Bob

anonimnystefy · 2012-03-02 08:12:18

So what if two brackets came together?

finitehelp · 2012-03-02 08:12:35

I am stuck again lol

finitehelp · 2012-03-02 08:25:52

I get p(x)^3-4/9

finitehelp · 2012-03-02 08:31:43

So I gues -4/9

finitehelp · 2012-03-02 08:55:29

I guess I keep ging in circles and coming back to 2/3 and i know that is wrong

Bob · 2012-03-02 09:42:07

Hi finitehelp

Which formula for standard deviation are you using? (i) or (ii) ?

Posts 32 and 33.

Bob

finitehelp · 2012-03-02 09:52:46

the first one

Bob · 2012-03-02 10:00:15

OK. So

Bob

hammana · 2012-03-05 08:38:24

There ae two basic rules in probability theory. If 2 events A and B with respective probabilities p and q are independent, the probability hat both happen in any order is the product pq. If they are not independent, the probability of A followed by B is the product of p by the probability of B, taking into account that A has occurred.

In the first cases, you have 2 independent events, Success (S in short) with probability 0.98 and Failure (F) with probability 002. After 2 tests there are 4 possibilities
S-S probabllity 0.98*0.98=0.9604
S-F 0.98*0.02=0.0196
F-S 0.02*0.98=0.0196
F-F 0.02*0.02=0.0004
Check that the sum is 1
In the second part events are Male (M) with probability 2/3 or Female with probability 1/3
if the first is a male ther remain 3 males ad 2 females. Now the probability of M is 3/5 and the probability of a female is 2/5. There fore the probability of M-M is 2/3*3/5=2/5.
Applying this youfind the following
M-M 2/3-3/5=2/5
M-F 2/3*2/5=4/15
F-F 1/3*1/4=1/12
F-m 1/3*3/4=1/4
Check again that the sum is 1

probabilities of the varaible x
probability of x=0 :2/5
" x=1 :4/15+1/4=31/60
" x=2 : 1/12
Total = 1

hammana · 2012-03-05 08:49:53

I am sorry, my previous table is wrong, it should be
M-M 1/3*3/5=6/15
M-F 1/3*2/5=4/15
F-F 1/3*1/5=1/15
F-M 1/3*4/5=4/15

hammana · 2012-03-05 09:01:15

There were still typing errors. Read
M-M 2/3*3/5=6/15
M-F 2/3*2/5=4/15
F-F 1/3*1/5=1/15
F-M 1/3*4/5=4/15

bobbym · 2012-03-05 09:02:24

Hi hammana;

You can use the edit button to edit a post. This makes it easier to read and follow.

hammana · 2012-03-05 09:05:47

I should correct the x table
x=0 if M-M probability 6/15
x=1 if M-F or F-M probability 4/15+4/15=8/15
x=2 if F-F probability 1/15

hammana · 2012-03-06 21:35:44

Hi bobbym
where is the edit button I can use to edit a post.

bobbym · 2012-03-06 21:42:10

Hi hammana;

Do you have that at the bottom of your posts?

Math Is Fun Forum

#26 2012-03-02 06:23:41

Re: Probability question help

#27 2012-03-02 06:25:27

Re: Probability question help

#28 2012-03-02 06:27:31

Re: Probability question help

#29 2012-03-02 06:35:34

Re: Probability question help

#30 2012-03-02 06:38:49

Re: Probability question help

#31 2012-03-02 06:39:50

Re: Probability question help

#32 2012-03-02 06:52:30

Re: Probability question help

#33 2012-03-02 06:57:30

Re: Probability question help

#34 2012-03-02 07:13:04

Re: Probability question help

#35 2012-03-02 07:21:46

Re: Probability question help

#36 2012-03-02 08:12:18

Re: Probability question help

#37 2012-03-02 08:12:35

Re: Probability question help

#38 2012-03-02 08:25:52

Re: Probability question help

#39 2012-03-02 08:31:43

Re: Probability question help

#40 2012-03-02 08:55:29

Re: Probability question help

#41 2012-03-02 09:42:07

Re: Probability question help

#42 2012-03-02 09:52:46

Re: Probability question help

#43 2012-03-02 10:00:15

Re: Probability question help

#44 2012-03-05 08:38:24

Re: Probability question help

#45 2012-03-05 08:49:53

Re: Probability question help

#46 2012-03-05 09:01:15

Re: Probability question help

#47 2012-03-05 09:02:24

Re: Probability question help

#48 2012-03-05 09:05:47

Re: Probability question help

#49 2012-03-06 21:35:44

Re: Probability question help

#50 2012-03-06 21:42:10

Re: Probability question help

Board footer