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#1 2010-03-20 16:43:18

soha
Real Member
Registered: 2006-07-07
Posts: 2,530

In a function..

In a function people greet themselves with shake hands. If the number of shake hands is
4950, then people present there are ------
A) 120 B) 110 C) 100 D) 90


"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!" smile smile
- David O. McKay

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#2 2010-03-20 18:23:45

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

Re: In a function..

Hi soha;

C) 100


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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#3 2010-03-21 02:40:08

soha
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Registered: 2006-07-07
Posts: 2,530

Re: In a function..

How did you get that ???? Please explain???


"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!" smile smile
- David O. McKay

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#4 2010-03-21 10:00:11

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

Re: In a function..

Hi soha;

The number of handshakes between n people is:

Solve for:

n = - 99 and n = 100 You can't have -99 people so n = 100


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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#5 2010-03-21 19:57:44

soha
Real Member
Registered: 2006-07-07
Posts: 2,530

Re: In a function..

we get n^2 - n -9900 = 0

after this..??


"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!" smile smile
- David O. McKay

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#6 2010-03-21 20:59:12

ZHero
Real Member
Registered: 2008-06-08
Posts: 1,889

Re: In a function..

Split the middle term (i.e. -n) as -100n and 99n and then factorize and equate to zero!
u'll get two values of n------->100 and -99.


big_smile


If two or more thoughts intersect, there has to be a point!

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#7 2010-03-29 23:07:24

soha
Real Member
Registered: 2006-07-07
Posts: 2,530

Re: In a function..

bobbym wrote:

Hi soha;

The number of handshakes between n people is:

how did you get this?


"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!" smile smile
- David O. McKay

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#8 2010-03-29 23:45:05

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

Re: In a function..

Hi soha;

Easiest way to understand this is the first person shakes 99 hands. The second person shakes 98 hands,The third person shakes 97 hands, the fourth person shakes 96 hands. until the 99th person, who only shakes the 100th hand . So there are

! + 2 + 3 + 4 + 5 + 6 + ... + 99 = 4950


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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#9 2010-04-01 02:51:45

soha
Real Member
Registered: 2006-07-07
Posts: 2,530

Re: In a function..

Why do we take that the first person shakes 99 hands ????

i mean , why 99 ? Why not any other number?


"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!" smile smile
- David O. McKay

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#10 2010-04-01 03:28:37

ZHero
Real Member
Registered: 2008-06-08
Posts: 1,889

Re: In a function..

soha wrote:

Why do we take that the first person shakes 99 hands ????

i mean , why 99 ? Why not any other number?

hi!!!!
Let the no. of people be X.
Hence, 1st person will shake hand with everybody else except He Himself i.e. X-1 people!
2nd will shake hand with X-2 people (not X-1 coz he's already shook hand with 1st!)!
and so on....
Hence, total no. of hand shakes=X+(X-1)+(X-2)+.....+3+2+1=4950!

Bobbym was just showing u that X=100 is the Right Answer!!
smile


If two or more thoughts intersect, there has to be a point!

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#11 2010-04-01 16:48:53

soha
Real Member
Registered: 2006-07-07
Posts: 2,530

Re: In a function..

x+ (x-1) +(x-2)+........... + 3+2+1=4950

how can we get x next ??


"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!" smile smile
- David O. McKay

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#12 2010-04-01 21:07:06

ZHero
Real Member
Registered: 2008-06-08
Posts: 1,889

Re: In a function..

soha wrote:

x+(x-1) +(x-2)+........... + 3+2+1=4950

how can we get x next ??

Sorry but in d above expression, first term X won't be there because first person shakes hand with X-1 people...
It shud be...
(X-1)+(X-2)+.......+3+2+1 which is the sum of first X-1 natural nos.
=

Hint:use formula for sum of X terms of an AP with first term 1 and Common Diff. 1.

Last edited by ZHero (2010-04-01 21:20:43)


If two or more thoughts intersect, there has to be a point!

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