# the last 2 probability questions

• Oct 20th 2008, 11:49 AM
Narek
the last 2 probability questions
give me hints so i will solve them by myself ...
Thank you a lot (Itwasntme)
• Oct 20th 2008, 12:01 PM
ddt
Quote:

Originally Posted by Narek
give me hints so i will solve them by myself ...
Thank you a lot (Itwasntme)

As Plato said before, please type them out - it's easier to quote and to follow the thread if there are more responses.

Nr. 46:
First: how many table arrangements with 8 people are there if the table were a long table (or if you want, a police line-up)?

Then, how many are the same if you take rotations at a round table into account?

Nr. 20:
In a polygon with n sides (n >= 3), a diagonal from edge-1 can go to which of the other edges?
• Oct 20th 2008, 12:26 PM
Narek
hmmm ...
still i dont get it! maybe a little more help please????? (Crying)
• Oct 20th 2008, 12:36 PM
ddt
Quote:

Originally Posted by Narek
still i dont get it! maybe a little more help please????? (Crying)

Nr. 46:
When you have a line of 8 people, in how many ways can you arrange those 8 people? That's step 1.

Nr. 20:
Take for instance a hexagon, i.e., a polygon with n=6 sides. It also has 6 corners. Take one of those corners. To how many other corners can you draw lines? How many of those lines are called diagonals?
• Oct 20th 2008, 03:02 PM
Narek

I draw it and I see that from any edge we can draw n/2 lines and from those only 1 is diagonal. I dont know how to show all these in mathematics language.

my problem about this question, is that I do NOT understand the questions even. its sad, but true. I dont understand what it says ...
is this solution true for this:

permulation WITHOUT repetition:

P(8,8) = 8! / (8-8)! = 40320
because of rotation we might have 40320 / 8 = 5040 different arrangements

True????
• Oct 20th 2008, 03:11 PM
ddt
Quote:

Originally Posted by Narek

I draw it and I see that from any edge we can draw n/2 lines and from those only 1 is diagonal. I dont know how to show all these in mathematics language.

No, a diagonal is any line from one corner to another corner which is not an edge.

Quote:

Originally Posted by Narek

my problem about this question, is that I do NOT understand the questions even. its sad, but true. I dont understand what it says ...
is this solution true for this:

permulation WITHOUT repetition:

P(8,8) = 8! / (8-8)! = 40320
because of rotation we might have 40320 / 8 = 5040 different arrangements

True????

That's true, for the part of putting 8 people in a line.
Now if you put them in a circle, there is no "first" person in the line. So, by rotating, how many of permutations are the same arrangement?
• Oct 20th 2008, 03:32 PM
Narek
Nr. 20)

so by mean of that, from every corner to others, there are n/2 lines. but there are lines which are repeated. how can i write this in mathematical language, and what to do with repeating lines?

Nr. 46)

P(8,8) = 8! / (8-8)! = 40320
because of rotation we might have 40320 / 8 = 5040 different arrangements

actually i divided the result by 8 so the problem goes around a circular table. I dont know what else should i do ... ????? (Itwasntme)
• Oct 20th 2008, 04:03 PM
ddt
Quote:

Originally Posted by Narek
Nr. 20)

so by mean of that, from every corner to others, there are n/2 lines. but there are lines which are repeated. how can i write this in mathematical language, and what to do with repeating lines?

Where did you get the formula n/2? From corner-2 there's an edge running to corner-1 and an edge to corner-3. The lines to the other corners are diagonals. That gives how many?

And how many times do you then count each line? Hint: a line has two endpoints...

Quote:

Originally Posted by Narek
Nr. 46)

P(8,8) = 8! / (8-8)! = 40320
because of rotation we might have 40320 / 8 = 5040 different arrangements

actually i divided the result by 8 so the problem goes around a circular table. I dont know what else should i do ... ????? (Itwasntme)