Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

**anna_gg****Member**- Registered: 2012-01-10
- Posts: 113

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?

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

Hi anna_gg;

**In mathematics, you don't understand things. You just get used to them.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

Offline

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,532

I got

.Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

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.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

Offline

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,532

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

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

Offline

**anna_gg****Member**- Registered: 2012-01-10
- Posts: 113

Excellent! Thanks!!

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

Hi anna_gg;

Where does the problem come from?

**In mathematics, you don't understand things. You just get used to them.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

Offline

**anna_gg****Member**- Registered: 2012-01-10
- Posts: 113

anonimnystefy wrote:

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

Offline

**anna_gg****Member**- Registered: 2012-01-10
- Posts: 113

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

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?

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

Offline

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,532

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.

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

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.

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

Offline

**anna_gg****Member**- Registered: 2012-01-10
- Posts: 113

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?

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

Hi;

That equals 5 / 24.

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

Offline

**anna_gg****Member**- Registered: 2012-01-10
- Posts: 113

anna_gg wrote:

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

Hi anna_gg;

Probably just a typo.

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

Offline

**anna_gg****Member**- Registered: 2012-01-10
- Posts: 113

bobbym wrote:

Hi anna_gg;

Probably just a typo.

Obviously, no worries

BTW my son got 2/5 on this question

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

Hi;

Is that good?

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

Offline

**anna_gg****Member**- Registered: 2012-01-10
- Posts: 113

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

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.

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

Offline

**anna_gg****Member**- Registered: 2012-01-10
- Posts: 113

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

Which one?

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

Offline

**anna_gg****Member**- Registered: 2012-01-10
- Posts: 113

bobbym wrote:

Which one?

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

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

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

Offline

**anna_gg****Member**- Registered: 2012-01-10
- Posts: 113

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.

Offline