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## #1 2012-07-04 07:11:22

anna_gg
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### Bus stop

A public bus arrives at the bus stop sometime between 6:00 and 6:30.
A passenger arrives at the same bus stop some random time within this time interval. What is the probability that the passenger catches the bus within 5 minutes from the time he arrives at the stop?

## #2 2012-07-04 09:35:25

bobbym
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### Re: Bus stop

Hi anna_gg;

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.

## #3 2012-07-04 09:43:21

anonimnystefy
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### Re: Bus stop

I got

.

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

## #4 2012-07-04 09:53:48

bobbym
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### Re: Bus stop

Hi anonimnystefy;

Yes, that is what I am getting now also. Very good!

Although this is a continuous probability we can model it with a discrete one.

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.

## #5 2012-07-04 10:41:01

anonimnystefy
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### Re: Bus stop

Last edited by anonimnystefy (2012-07-05 03:04:28)

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

## #6 2012-07-04 20:02:45

anna_gg
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### Re: Bus stop

Excellent! Thanks!!

## #7 2012-07-04 20:03:37

bobbym
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### Re: Bus stop

Hi anna_gg;

Where does the problem come from?

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.

## #8 2012-07-04 20:47:28

anna_gg
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### Re: Bus stop

#### anonimnystefy wrote:

Are you sure the result is 1/72? I am getting 15/72!

## #9 2012-07-04 20:50:43

anna_gg
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### Re: Bus stop

#### bobbym wrote:

Hi anna_gg;

Where does the problem come from?

It was in one of my son's final exams in high school. Obviously he did it all wrong - he got 1/6

## #10 2012-07-04 22:17:29

bobbym
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### Re: Bus stop

Hi anna_gg;

That is what I got at first too. Did they give him some partial credit for getting the same answer as I did?

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.

## #11 2012-07-04 22:46:41

anonimnystefy
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### Re: Bus stop

Hi anna_gg

My answer is 11/72 and not 1/72 and it is same as bobbym's so I deduce that it is correct.

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

## #12 2012-07-04 23:02:25

bobbym
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### Re: Bus stop

Hi anna_gg;

Anonimnystefy's answer is 11 / 72 not 1 / 72. I am pretty sure that it is the correct answer because it can be derived in 3 different ways.

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.

## #13 2012-07-05 01:41:33

anna_gg
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### Re: Bus stop

#### bobbym wrote:

Hi anna_gg;

Anonimnystefy's answer is 11 / 72 not 1 / 72. I am pretty sure that it is the correct answer because it can be derived in 3 different ways.

Sorry, that's what I meant, 11/72. I am just saying that:

5/6 * 1/6 + 1/6 * 5/12=15/72, isn't it?

## #14 2012-07-05 01:45:06

bobbym
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### Re: Bus stop

Hi;

That equals 5 / 24.

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.

## #15 2012-07-05 01:57:15

anna_gg
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### Re: Bus stop

#### bobbym wrote:

Hi anna_gg;

Anonimnystefy's answer is 11 / 72 not 1 / 72. I am pretty sure that it is the correct answer because it can be derived in 3 different ways.

Sorry, that's what I meant, 11/72. I am just saying that:

5/6 * 1/6 + 1/6 * 5/12=15/72, isn't it?

OK got it:
Anonimnystefy, it's 5/6 * 1/6 + 1/6 * 1/12 (and not 5/12)=11/72

The area of the triangle you are referring to, is (1/6 * 5/30)/2 = 1/6 * 1/12

## #16 2012-07-05 02:09:36

bobbym
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### Re: Bus stop

Hi anna_gg;

Probably just a typo.

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.

## #17 2012-07-05 02:16:46

anna_gg
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### Re: Bus stop

#### bobbym wrote:

Hi anna_gg;

Probably just a typo.

Obviously, no worries

BTW my son got 2/5 on this question

## #18 2012-07-05 02:20:02

bobbym
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### Re: Bus stop

Hi;

Is that good?

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.

## #19 2012-07-05 02:31:23

anna_gg
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### Re: Bus stop

NO He got 2 points out of 5 for this question... That's the partial credit you were referring to...

## #20 2012-07-05 02:35:03

bobbym
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### Re: Bus stop

Sorry to hear that. Probability problems are tough for everybody, tell him not to feel bad. Personally, I feel the problem is too strong for high school.

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.

## #21 2012-07-05 03:32:57

anna_gg
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### Re: Bus stop

#### bobbym wrote:

Sorry to hear that. Probability problems are tough for everybody, tell him not to feel bad. Personally, I feel the problem is too strong for high school.

Not if you are a candidate to the polytechnic

## #22 2012-07-05 03:35:00

bobbym
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### Re: Bus stop

Which one?

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.

## #23 2012-07-05 04:05:43

anna_gg
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### Re: Bus stop

#### bobbym wrote:

Which one?

In Greece - National Technical University of Athens. We are Greeks

## #24 2012-07-05 04:09:19

bobbym
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### Re: Bus stop

Very good! You must be very proud of him. What would he like to do as his life's work?

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.

## #25 2012-07-05 04:26:59

anna_gg
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### Re: Bus stop

#### bobbym wrote:

Very good! You must be very proud of him. What would he like to do as his life's work?

He wants to become a mechanical or electrical engineer.

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