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

You are not logged in.

- Topics: Active | Unanswered

**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,228

If you can get Dave tv then I recommend this programme on Mondays at 8pm. Like most Dave programmes it is repeated many times during the week.

Meanwhile back to my problem.

One of the puzzles is this.

A town has a grid road system and there are five groups of students at the grid locations shown in my diagram. The red numbers show how many students there are at each location. eg. There are 5 students at (3,7).

The students want to meet up at a grid point. They can only walk along the grid lines. Where should they agree to meet so that the total distance walked by all 13 of them is a minimum?

Now Marcus du Sautoy poses this puzzle to Dara O'Briain and Alex Horne. He declares that Dara's answer is not correct. **I think he is wrong!**

As Marcus (OBE) is a Professor of Mathematics at the University of Oxford I thought I'd better get a second opinion.

Anyone care to try the puzzle and help me out?

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,037

Sure thing! Give us some time.

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

The knowledge of some things as a function of age is a delta function.

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi bob bundy;

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,228

hi bobbym,

Thanks for joining in. Please would you post the coordinates for this answer.

Thanks,

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

(3,5)

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,037

The smallest I have gotten so far is 58.

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

The knowledge of some things as a function of age is a delta function.

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,037

Hi bobbym

For that point I get 58.

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

The knowledge of some things as a function of age is a delta function.

Offline

**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,228

hi

(3,5) ?

I make that a distance of 5 x 2 + 2 x 3 + 2 x 4 + 3 x 8 + 2 x 5 = 58.

Stefy: What coordinates please?

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Yes, 58 is smallest. there are 14 students not 13 as you indicate. (3,3) is the spot. Sorry, I did not see that earlier.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,037

I get 58 for:

(3,3)

(3,4)

(3,5)

(4,3)

(4,4)

(4,5)

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

The knowledge of some things as a function of age is a delta function.

Offline

**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,228

How can I have missed that? I'm sure that was how the puzzle was set and 13 was the number. At no time did I bother to count them!

What are you getting for the distance for (3,3) ?

Oh I see 58. I think I need glasses!

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

All of these are 58.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,037

There is a lot of them.

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

The knowledge of some things as a function of age is a delta function.

Offline

**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,228

Ok. Enough. Thank you so much.

In the programme Marcus uses a 'method' to calculate the optimum position and declares it to be (5,5). As it happens the guest Alex gets this and so is declared the winner. Dara, the presenter, gets (5,3) and is declared wrong.

I agree that there are many possible best answers, all giving 58, so thank you for comfirming that. I'm just wondering, in view of the 13, 14 doubt, whether I made up a student. The programme is repeated tonight so I'm going to watch it again. I'll post some more tomorrow.

Thank you for your help.

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

No, just 9.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,037

That is a lot,bobbym.

Okay,tell us what happened.Maybe we can sue them.

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

The knowledge of some things as a function of age is a delta function.

Offline

**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,228

OK. Now I'm admitting to being doubly stupid.

(i) I recorded the programme on my pvr so I don't need to wait.

(ii) There are 13 students as shown on the revised diagram below.

So sorry.

Bob

ps. Tt's a good programme if you can get it. There may be some U tube clips.

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

If you reduce the number of students at (3,7) to 4 you will get a unique answer.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Mine is better, there are still 2 solutions!

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,228

Did you see post #17 ?

That's the corrected diagram.

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

I see it now there is only one solution now! Thanks for posting that.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,228

Which is?

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,037

Hi Bob

I got 51 at (5,5).I think the guys who said that might be correct.

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

The knowledge of some things as a function of age is a delta function.

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Looks like (5,5) for 51.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,037

Yup.Since we got 58 everywhere,we just subtract the taxicab distance of the student who is alone from the total distance and we get that of all those that had the distance 58,the smallest one is when we subtract 7.

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

The knowledge of some things as a function of age is a delta function.

Offline