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OfflineNuggetpouch
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elementary statistitcs question. plz HELP!
    #11272186 - 10/18/09 06:11 PM (8 years, 1 day ago)

i have a mid-term tomorrow and i'm looking at one of the questions on the study guide, the answer is not provided so there's no way of knowing if i did the question right. can anyone answer it for me so we can compare our answers?

The question is: 50 marbles are in a jar; 5 white; 4 pink; 41 gray. If 2 marbles are drawn out at random, without replacement, what is the probability of getting one white marble and one pink marble?

Plzzzz save my ass


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Offlinelearningtofly
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Re: elementary statistitcs question. plz HELP! [Re: Nuggetpouch]
    #11272206 - 10/18/09 06:15 PM (8 years, 1 day ago)

4/490


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OfflineJair
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Re: elementary statistitcs question. plz HELP! [Re: Nuggetpouch]
    #11272210 - 10/18/09 06:16 PM (8 years, 1 day ago)

Let's see.

You are looking for a white and a pink marble.  So S=[PW] + [WP].  These are the only combinations you can have of white and pink marbles with only two draws.  But WP and PW are different, so be sure to include both. 

P(P)= 4/50
P(W)= 5/50

S=[4/50 x 5/50] + [5/50 x 4/50]

The answer is .016 or 1.6%


--------------------


Edited by Jair (10/18/09 06:17 PM)


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OfflineNuggetpouch
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Re: elementary statistitcs question. plz HELP! [Re: learningtofly]
    #11272212 - 10/18/09 06:16 PM (8 years, 1 day ago)

hmm i got 20/2450, which i guess is an un-simplified version of your answer.... can we verify that this is correct?

EDIT: yeah i dont think this is right....


--------------------
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Edited by Nuggetpouch (10/18/09 06:18 PM)


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Offlinelearningtofly
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Re: elementary statistitcs question. plz HELP! [Re: Jair]
    #11272219 - 10/18/09 06:18 PM (8 years, 1 day ago)

Quote:

Jair said:
Let's see.

You are looking for a white and a pink marble.  So S=[PW] + [WP].  These are the only combinations you can have of white and pink marbles with only two draws.  But WP and PW are different, so be sure to include both. 

P(P)= 4/50
P(W)= 5/50

S=[4/50 x 5/50] + [5/50 x 4/50]

The answer is .016 or 1.6%




did you account for w/out replacement????????????!?!??!??!


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OfflineJair
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Re: elementary statistitcs question. plz HELP! [Re: learningtofly]
    #11272224 - 10/18/09 06:19 PM (8 years, 1 day ago)

Quote:

learningtofly said:
Quote:

Jair said:
Let's see.

You are looking for a white and a pink marble.  So S=[PW] + [WP].  These are the only combinations you can have of white and pink marbles with only two draws.  But WP and PW are different, so be sure to include both. 

P(P)= 4/50
P(W)= 5/50

S=[4/50 x 5/50] + [5/50 x 4/50]

The answer is .016 or 1.6%




did you account for w/out replacement????????????!?!??!??!




DOH, I thought it said with replacement, sorry OP I'm stoned.


--------------------


Edited by Jair (10/18/09 06:19 PM)


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OfflineNuggetpouch
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Re: elementary statistitcs question. plz HELP! [Re: Jair]
    #11272225 - 10/18/09 06:19 PM (8 years, 1 day ago)

Quote:

Jair said:
Let's see.

You are looking for a white and a pink marble.  So S=[PW] + [WP].  These are the only combinations you can have of white and pink marbles with only two draws.  But WP and PW are different, so be sure to include both. 

P(P)= 4/50
P(W)= 5/50

S=[4/50 x 5/50] + [5/50 x 4/50]

The answer is .016 or 1.6%




You forget that there is no replacement, you really did help clear things up for me with the sample space but it would actually be [4/50 x 5/49] + [5/50 x 4/49]


--------------------
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OfflineJair
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Re: elementary statistitcs question. plz HELP! [Re: Nuggetpouch]
    #11272233 - 10/18/09 06:20 PM (8 years, 1 day ago)

Quote:

Nuggetpouch said:
Quote:

Jair said:
Let's see.

You are looking for a white and a pink marble.  So S=[PW] + [WP].  These are the only combinations you can have of white and pink marbles with only two draws.  But WP and PW are different, so be sure to include both. 

P(P)= 4/50
P(W)= 5/50

S=[4/50 x 5/50] + [5/50 x 4/50]

The answer is .016 or 1.6%




You forget that there is no replacement, you really did help clear things up for me with the sample space but it would actually be [4/50 x 5/49] + [5/50 x 4/49]




Yeah, I thought it said with replacement, sorry!


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OfflineJair
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Re: elementary statistitcs question. plz HELP! [Re: Jair]
    #11272256 - 10/18/09 06:23 PM (8 years, 1 day ago)

I still got the same answer.


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OfflineNuggetpouch
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Re: elementary statistitcs question. plz HELP! [Re: Jair]
    #11272259 - 10/18/09 06:23 PM (8 years, 1 day ago)

Quote:

Jair said:
Let's see.

You are looking for a white and a pink marble.  So S=[PW] + [WP].  These are the only combinations you can have of white and pink marbles with only two draws.  But WP and PW are different, so be sure to include both. 

P(P)= 4/50
P(W)= 5/50

S=[4/50 x 5/50] + [5/50 x 4/50]

The answer is .016 or 1.6%




oh and what does S stand for again?

thx for all your helps by the way


--------------------
My statistical assumption is that chemical tapering should begin when the rate of visiting ODD exceeds the rate of visiting Pub, or any other Shroomery forum.


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OfflineJair
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Re: elementary statistitcs question. plz HELP! [Re: Nuggetpouch]
    #11272263 - 10/18/09 06:25 PM (8 years, 1 day ago)

Quote:

Nuggetpouch said:
Quote:

Jair said:
Let's see.

You are looking for a white and a pink marble.  So S=[PW] + [WP].  These are the only combinations you can have of white and pink marbles with only two draws.  But WP and PW are different, so be sure to include both. 

P(P)= 4/50
P(W)= 5/50

S=[4/50 x 5/50] + [5/50 x 4/50]

The answer is .016 or 1.6%




oh and what does S stand for again?

thx for all your helps by the way




My professor is Asian and I can't really understand her so I just copy what she has on the board, and she uses "S."  I'm pretty sure it means sample or sample space though.


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OfflineNuggetpouch
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Re: elementary statistitcs question. plz HELP! [Re: Jair]
    #11272274 - 10/18/09 06:26 PM (8 years, 1 day ago)

Quote:

Jair said:
I still got the same answer.





yeah your right... the answer is still 1.6% even if you do it without replacement... thats weird.... i guess that 1 extra marble not being accounted for is just too insignificant to change the answer anything worth not rounding :shrug:


--------------------
My statistical assumption is that chemical tapering should begin when the rate of visiting ODD exceeds the rate of visiting Pub, or any other Shroomery forum.


Edited by Nuggetpouch (10/18/09 06:29 PM)


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OfflineNuggetpouch
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Re: elementary statistitcs question. plz HELP! [Re: learningtofly]
    #11272283 - 10/18/09 06:28 PM (8 years, 1 day ago)

Quote:

learningtofly said:
4/490




and is this even corerct? i think the correct answer simplified is actually 4/245... you forgot to account for the fact that there are TWO possible ways to get a white and a pink. you can get a white on the first and a pink on the second OR a pink on the first and a white on the second... am i right on this?

i think im finally starting to get it :smile:


--------------------
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OfflineJair
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Re: elementary statistitcs question. plz HELP! [Re: Nuggetpouch]
    #11272297 - 10/18/09 06:31 PM (8 years, 1 day ago)

Quote:

Nuggetpouch said:
Quote:

learningtofly said:
4/490




and is this even corerct? i think the correct answer simplified is actually 4/245... you forgot to account for the fact that there are TWO possible ways to get a white and a pink. you can get a white on the first and a pink on the second OR a pink on the first and a white on the second... am i right on this?

i think im finally starting to get it :smile:




4/245 is correct, and you are right on the different combinations.  I don't ever think about the big picture though- you could make a tree diagram and see what you need, just too much work.


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OfflineNuggetpouch
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Re: elementary statistitcs question. plz HELP! [Re: Nuggetpouch]
    #11272302 - 10/18/09 06:33 PM (8 years, 1 day ago)

also i need help with 1 more question.

50 marbles are in a jar; 5 are white, 25 are black, 10 are blue, 6 are orange, and 4 are pink. If 2 marbles are drawn out and random, without replacement, what is

a) the probability of getting at most one white marble?

b) the probability of getting no white marbles if the first marble drawn is orange?


--------------------
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OfflineNeuron
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Re: elementary statistitcs question. plz HELP! [Re: Nuggetpouch]
    #11272365 - 10/18/09 06:46 PM (8 years, 1 day ago)

The math textbook you have should have examples of each kind of problem...


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OfflineJair
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Re: elementary statistitcs question. plz HELP! [Re: Nuggetpouch]
    #11272373 - 10/18/09 06:47 PM (8 years, 1 day ago)

Quote:

Nuggetpouch said:
also i need help with 1 more question.

50 marbles are in a jar; 5 are white, 25 are black, 10 are blue, 6 are orange, and 4 are pink. If 2 marbles are drawn out and random, without replacement, what is

a) the probability of getting at most one white marble?

b) the probability of getting no white marbles if the first marble drawn is orange?





Ahh, this is more fun!

a) "At most one white marble" includes 1 white marble and no white marbles. That is a lot of combinations to think of so use this trick:  1-(Ac).  For this complementary thing, you are finding what it ISN'T asking for and subtract from one.  Your sample space has to be S=[WW].  Any other combination includes 1 or 0 whites so we can't use those.

P(W)= 5/50

S=1 - [5/50 x 5/49]

Answer: .01 or 1%

b) Ok so Orange is always first in your samples for this question and you can't have any whites.  S=[OBla] + [OBlu] + [OO] + [OP]

P(O}= 6/50
P(Bla)= 25/50
P(Blu)= 10/50
P(P)= 4/50

S=[6/50 x 25/49] + [6/50 x 25/49] + [6/50 x 6/49] + [6/50 x 4/49]

Answer: Don't want to do this on my computer calculator.

THIS MIGHT NOT ALL BE CORRECT, I AM REALLY HIGH!


--------------------


Edited by Jair (10/18/09 07:01 PM)


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Offlinelearningtofly
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Re: elementary statistitcs question. plz HELP! [Re: Jair]
    #11272474 - 10/18/09 07:10 PM (8 years, 1 day ago)

Quote:

Jair said:
Quote:

Nuggetpouch said:
Quote:

Jair said:
Let's see.

You are looking for a white and a pink marble.  So S=[PW] + [WP].  These are the only combinations you can have of white and pink marbles with only two draws.  But WP and PW are different, so be sure to include both. 

P(P)= 4/50
P(W)= 5/50

S=[4/50 x 5/50] + [5/50 x 4/50]

The answer is .016 or 1.6%




oh and what does S stand for again?

thx for all your helps by the way




My professor is Asian and I can't really understand her so I just copy what she has on the board, and she uses "S."  I'm pretty sure it means sample or sample space though.




generally N is population and n is sample.


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OfflineNuggetpouch
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Re: elementary statistitcs question. plz HELP! [Re: learningtofly]
    #11272502 - 10/18/09 07:15 PM (8 years, 1 day ago)

Okay, I have one last question and I just wanted to see if my answers were correct.

25 planes approaching earth, each plane is programmed to randomly select one of two airports and land at it, the airports are aplha and beta.

A) What is the probability that all 25 planes land at site aplha?

B) What is the probability that at least 1 plane lands at site alpha?


:thanx:


--------------------
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OfflineJair
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Re: elementary statistitcs question. plz HELP! [Re: Nuggetpouch]
    #11272584 - 10/18/09 07:28 PM (8 years, 1 day ago)

Quote:

Nuggetpouch said:
Okay, I have one last question and I just wanted to see if my answers were correct.

25 planes approaching earth, each plane is programmed to randomly select one of two airports and land at it, the airports are aplha and beta.

A) What is the probability that all 25 planes land at site aplha?

B) What is the probability that at least 1 plane lands at site alpha?


:thanx:




A) 1/2 to the power of 25 because S=[AAAAAAAAAAAAAAAAAAAAAAAAA]

and P(A)= 1/2

B) Do the opposite trick again. 1-(Ac).  "At least one plane at alpha" includes everything but 0 alphas.  This is S=[B to the power of 25].  Since both A^25 and B^25 are P= 1/2, you can just subtract your answer from question A from one.

1-B^25.

Edit: Make sure you finish out the problem, I just didn't have my calc around.


--------------------


Edited by Jair (10/18/09 07:29 PM)


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