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Topic review (newest first)

bobbym
2012-12-18 11:37:13

Hi;

I agree.

scientia
2012-12-18 11:30:56

bobbym wrote:

You can't do that as that allows for possibilities in which there's a girl at both ends

Not at the same time!

Exactly. Jacks's method allows girls to be at boths ends at the same tiem that was where his proof went wrong.

He wanted us to tell him where his proof went wrong, didn't he?

bobbym
2012-12-18 11:19:42

Hmmmm. I know that. I know that you kid but you do not joke.

anonimnystefy
2012-12-18 11:15:45

I was just kidding!

bobbym
2012-12-18 11:14:42

Point is, sometimes it is a guy and sometimes it is not. Depending on what slot the last guy goes into.

anonimnystefy
2012-12-18 11:10:53

Well, maybe the girls at the ends are in a superposition and our observation force the situation to enter one of the two possible states. smile

bobbym
2012-12-18 11:07:45

You can't do that as that allows for possibilities in which there's a girl at both ends

Not at the same time!

jacks
2012-12-18 04:42:01

Thanks bobbym and scientia.

but i did not understand the meaning of

You can't do that as that allows for possibilities in which there's a girl at both ends

scientia
2012-12-18 03:11:10

jacks wrote:

But where i have done mistake in my solution.

Your mistake is in

jacks wrote:

now arrange girls in 7 gaps ,


You can't do that as that allows for possibilities in which there's a girl at both ends, which you don't want. The possibilities are either

X_X_X_X_X_X_

or

_X_X_X_X_X_X

Each set has
ways; hence there are
ways altogether.

bobbym
2012-12-18 03:06:22

Arrange the girls first in a line;

_ G _ G _  G _ G _ G _  G _  = 6!

In the first _ 6 boys can go

_ G (6 boys ) G _  G _ G _ G _  G _

In the second 5 boys

_ G (6 boys ) G (5 boys )  G _ G _ G _  G _

all the way down to

_ G (6 boys ) G (5 boys )  G (4 boys) G (3 boys) G (2 boys)  G _

That can be done in 6 x 5 x 4 x 3 x 2 = 6!

So far we have 6! * 6!, now the last two slots

_ G (6 boys ) G (5 boys )  G (4 boys) G (3 boys) G (2 boys)  G _

the one remaining boy can go in 2 ways.

2 * 6! * 6!

jacks
2012-12-18 02:56:01

Yes bobbym you are right.

But where i have done mistake in my solution.

bobbym
2012-12-18 02:49:35

Hi;

I am getting 2 * 6! * 6! as the answer. Provided we are assuming the girls and boys are distinct which is reasonable.

jacks
2012-12-18 02:35:52

6 boys and 6 girls are sitting in a row . Then the no. of ways  that boys and girls sits alternatively

my solution::

Using gap method::

here X  = denote boys and _ = denote girl

Then X _ X _  X _ X _  X _ X _

first we can arrange boys , which can be done in 6! ways

now arrange girls in 7 gaps ,

for that first we select 6 place out of 7 which can be  done in C (7,6) ways and now arrange these 6 girls

Which can we done in C(7,6) * 6! = 7!

So total no. of ways is = 6! * 7!

but answer is = 2*6! *6!

so where i have done mistake

Thanks

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