Math Is Fun Forum
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#26 2014-08-10 00:33:44
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: What am I doing wrong? #Coordinate_Geometry
Hi;
There are 11 men + 2 women = 13 players.
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.
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#27 2014-08-10 01:40:43
Re: What am I doing wrong? #Coordinate_Geometry
Oh no! Silly mistake
'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'
I'm not crazy, my mother had me tested.
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#28 2014-08-10 02:29:15
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: What am I doing wrong? #Coordinate_Geometry
What silly mistake?
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.
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#29 2014-08-10 03:05:49
Re: What am I doing wrong? #Coordinate_Geometry
What should be my equation?
'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'
I'm not crazy, my mother had me tested.
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#30 2014-08-10 03:08:18
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: What am I doing wrong? #Coordinate_Geometry
n(n-1) - 4n = 66
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.
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#31 2014-08-10 03:32:57
Re: What am I doing wrong? #Coordinate_Geometry
n=var('n');
solve(66+(4*n)==2*binomial(n,2),[n])Why do you multiply it with 4 and not 8?
'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'
I'm not crazy, my mother had me tested.
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#32 2014-08-10 03:47:24
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: What am I doing wrong? #Coordinate_Geometry
EM of course!
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.
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#33 2014-08-10 03:50:16
Re: What am I doing wrong? #Coordinate_Geometry
-_- What has it got to with EM?
'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'
I'm not crazy, my mother had me tested.
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#34 2014-08-10 04:10:27
- Bob
- Administrator
- Registered: 2010-06-20
- Posts: 10,140
Re: What am I doing wrong? #Coordinate_Geometry
hi Agnishom,
I've only just caught up with this one.
First thing I did is (I claim) EM. I put your line and points onto a graph. So I knew straight away that your coordinates weren't correct. Took a while to find the error though.
Recommendation: Always make a picture (graph in this case). Even a rough sketch would be enough to show you there must be an error somewhere. I find them all the time in my posts. Mostly before Stefy spots them. 
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
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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#35 2014-08-10 04:15:08
Re: What am I doing wrong? #Coordinate_Geometry
Hi bob;
The first question is age old. Would you please help me with this one?
I need a solution to this:
There were two women participating in a chess tournament. Every participant played two games with the other participants. The number of games that men played between themselves proved to exceed by 66 the number of games that the men played with the women. How many men were there?
'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'
I'm not crazy, my mother had me tested.
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#36 2014-08-10 05:18:25
- Bob
- Administrator
- Registered: 2010-06-20
- Posts: 10,140
Re: What am I doing wrong? #Coordinate_Geometry
hi Agnishom,
Cannot think of a picture for this. I'm confident you know what women look like.
Let the number of men be n.
man v man matches:
Each man must play the other n-1 men. But twice. But each match gets counted twice; once for A v B and then again for B v A so divide by 2 for that.
Total = n x (n-1) x 2 / 2 =n^2 - n
woman v man matches:
Note: this is the same as the number of matches the men play against the women.
Each woman must play n men, twice. There is no reason to divide this by two since I'm not counting these matches any other way.
Total = 2n x 2 = 4n
So we have n^2 - n = 4n + 66 => n^2 - 5n - 66 = 0 => (n+6)(n-11) = 0. Discard the negative solution and we have number of men = 11.
Check. 11 men will play 11 x 10 x 2 / 2 = 110 matches against men and 11 x 2 x 2 = 44 matches against women. 110 - 44 = 66.
Bob
ps. Is the questioner trying to imply that chess is mainly played by men. Tut tut! I suppose the others were too busy making the tea.
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
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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#37 2014-08-10 05:35:26
Re: What am I doing wrong? #Coordinate_Geometry
Hi bob;
Thanks a lot.
What does this mean:
Every participant played two games with the other participants.
'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'
I'm not crazy, my mother had me tested.
Offline
#38 2014-08-10 06:42:01
- Bob
- Administrator
- Registered: 2010-06-20
- Posts: 10,140
Re: What am I doing wrong? #Coordinate_Geometry
hi
At last a chance to make a diagram.
defn: participant = a chess player, male or female, who takes part in the tournament.
In this diagram the black dots represent participants and each red line represents a match between two participants. With 5 participants there are 20 matches.
Hope that makes it clear.
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
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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#39 2014-08-10 07:58:36
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: What am I doing wrong? #Coordinate_Geometry
-_- What has it got to with EM?
The purpose of computing is insight, not numbers.
This provides the insight.
s = Permutations[{a, b, c, d, e, 1, 2}, {2}]
(Cases[s, {m_, a_} /; NumericQ[a] == False && NumericQ[m] == True] // Length)The number of games the guys play with the gals is 4n. The number of games they play with each other is n(n-1).
n(n-1) - 4n = 66
Solve the quadratic, n = 11.
n + 2 = 13
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.
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