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## #1 2014-05-16 14:01:35

Delsa
Member
Registered: 2014-05-16
Posts: 2

### Probability Problems

Hi!

I am currently taking Probability and Statistics subject at a university and I find your page very helpful.  I actually find it more comprehensible than our discussions at the university.  I would like to thank you for all these materials on probability and statistics.  They have helped me a lot and I understood most of my lessons with your help.

However, I have a couple of problems which I did not find in any of the examples you have provided and I don`t know how to do them.  Can you please take a look and help me solve and understand them?

Problem 1:  The probability that a patient recovers from a rare blood disease is 0.4.  If 15 people are known to have contracted this disease, what is the probability that
a.  at least 10

survive?
b.  from 3 to 8 survive?
c.  exactly 5 survive?

Problem 2:  On average a certain intersection results in 3 traffic accidents per month.  What is the probability that for any given month at this intersection
a. exactly 5 accidents will occur?
b. less than 3 accidents will occur?
c. at least 2 accidents will occur?

I would greatly appreciate your help regarding my problem.  Thank you very much and more power!

Sincerely,
Delsa

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## #2 2014-05-16 14:08:40

ShivamS
Member
Registered: 2011-02-07
Posts: 3,518

### Re: Probability Problems

Welcome to the forum, Delsa.

Problem 1.
(a)  Pr(X=5) = 20!/{15!5!} (0.4)5(1-0.4)15 = 0.0746
or   Pr(X=5) = Pr(X<=5) - Pr(X<=4) = 0.1256 - 0.0510 = 0.0746

(b) Pr(3<=X<=8) = Pr(X<=8) - Pr(X<3) = Pr(X<=8) - Pr(X<=2) = 0.5956 - 0.0036 = 0.5920

(c) Pr(X>=10) = 1 - Pr(X<10) = 1 - Pr(X<=9) = 1 - 0.7553 = 0.2447

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## #3 2014-05-16 14:27:01

Delsa
Member
Registered: 2014-05-16
Posts: 2

### Re: Probability Problems

Thank you for the welcome.  And thank you for such a fast reply too.

I have been reading and searching for days on ends that I have thought of asking for help as a last resort.  But now, i realized, I need more reading and I really need to work harder.

Thank you very much and more power!

Sincerely,
Delsa

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## #4 2014-05-17 00:43:41

ShivamS
Member
Registered: 2011-02-07
Posts: 3,518

### Re: Probability Problems

Why does it not say "last edited ..."?

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## #5 2014-05-17 00:44:45

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,512

### Re: Probability Problems

Hi;

Where should it say that?

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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## #6 2014-05-17 00:50:52

ShivamS
Member
Registered: 2011-02-07
Posts: 3,518

### Re: Probability Problems

Under her [Delsa's] last post.

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## #7 2014-05-17 00:52:59

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,512

### Re: Probability Problems

Did she edit it?

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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## #8 2014-05-17 00:55:04

ShivamS
Member
Registered: 2011-02-07
Posts: 3,518

Yes.

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## #9 2014-05-17 00:57:15

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,512

### Re: Probability Problems

That I can not explain, the forum does have its quirks. That is why it needs the upgrade.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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## #10 2014-05-17 04:00:19

ShivamS
Member
Registered: 2011-02-07
Posts: 3,518

### Re: Probability Problems

Delsa wrote:

I have been reading and searching for days on ends that I have thought of asking for help as a last resort.  But now, i realized, I need more reading and I really need to work harder.

You're welcome.

It is important, especially in mathematics, to make sure that you actually know the concepts. Otherwise, you will not generally succeed on the more difficult problems. But you should not be worried about asking trivial questions or asking about minor conceptual misunderstandings here, because we don't mind it.

Delsa wrote:

And thank you for such a fast reply too.

There usually are several members online who can help you (especially one of the of the administrators, bobbym) so you will get fast replies most of the time.

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## #11 2014-05-17 23:20:51

ShivamS
Member
Registered: 2011-02-07
Posts: 3,518

### Re: Probability Problems

Here is a creepy story: last night I had a dream that Delsa had posted here saying she hadn't editted her post... It was so realistic that I came to this thread thinking I would reply to her post!

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## #12 2014-05-17 23:22:58

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,512

### Re: Probability Problems

Yes, that happened but was lost in the upgrade.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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## #13 2014-05-17 23:24:46

ShivamS
Member
Registered: 2011-02-07
Posts: 3,518

### Re: Probability Problems

Wait, she actually posted that? I remember you replying something too... Then it wasn't a dream?

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## #14 2014-05-17 23:25:44

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,512

### Re: Probability Problems

I thought you meant that she had edited a post and the message was left out. But she said she never edited the post.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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## #15 2014-05-17 23:28:31

ShivamS
Member
Registered: 2011-02-07
Posts: 3,518

### Re: Probability Problems

Then it was a dream.

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## #16 2014-05-17 23:33:43

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,512

### Re: Probability Problems

A dream of a real event.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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## #17 2014-05-18 02:40:29

Agnishom
Real Member
From: The Complex Plane
Registered: 2011-01-29
Posts: 15,891
Website

### Re: Probability Problems

I've not read the whole thread but do you really dream of the forum?

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Humanity is still kept intact. It remains within.' -Alokananda

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## #18 2014-05-18 02:51:01

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,512

### Re: Probability Problems

I dream of verdant pastures and gladen woods where I may battle the last reppie I will ever see.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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## #19 2014-05-18 02:56:40

ShivamS
Member
Registered: 2011-02-07
Posts: 3,518

### Re: Probability Problems

Agnishom wrote:

I've not read the whole thread but do you really dream of the forum?

Not too often, but yes. I was on the forum for a long time yesterday, so maybe that is why.

Last edited by ShivamS (2014-05-18 02:57:10)

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## #20 2014-05-18 03:05:28

Agnishom
Real Member
From: The Complex Plane
Registered: 2011-01-29
Posts: 15,891
Website

### Re: Probability Problems

I recently had a dream on how I missed my school bus while I was busy repairing my bicycle and then I got on a train which took me to a far away station. When I came back home, my uncle, who happens to be a philosophy professor explained me the legal problems of owning that bicycle. Also, I remember folding the bicycle into parts like an umbrella

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Humanity is still kept intact. It remains within.' -Alokananda

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## #21 2014-05-18 03:06:36

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,512

### Re: Probability Problems

Are all your relatives teachers or professional people?

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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## #22 2014-05-18 03:09:06

ShivamS
Member
Registered: 2011-02-07
Posts: 3,518

### Re: Probability Problems

The day before yesterday I had a dream that my children were killed. My dreams are usually weird.

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## #23 2014-05-18 03:11:13

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,512

### Re: Probability Problems

But you do not have any children so it is just a dream.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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## #24 2014-05-18 03:14:47

Agnishom
Real Member
From: The Complex Plane
Registered: 2011-01-29
Posts: 15,891
Website

### Re: Probability Problems

I too do not have a railway station near my nearest grocery, Its just a dream too.

Who are proffessional people?

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Humanity is still kept intact. It remains within.' -Alokananda

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## #25 2014-05-18 03:18:35

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,512

### Re: Probability Problems

People who have good jobs, doctors, teachers, engineers etc.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Offline