Jump to content


Welcome to BrainDen.com - Brain Teasers Forum

Welcome to BrainDen.com - Brain Teasers Forum. Like most online communities you must register to post in our community, but don't worry this is a simple free process. To be a part of BrainDen Forums you may create a new account or sign in if you already have an account.
As a member you could start new topics, reply to others, subscribe to topics/forums to get automatic updates, get your own profile and make new friends.

Of course, you can also enjoy our collection of amazing optical illusions and cool math games.

If you like our site, you may support us by simply clicking Google "+1" or Facebook "Like" buttons at the top.
If you have a website, we would appreciate a little link to BrainDen.

Thanks and enjoy the Den :-)
Guest Message by DevFuse
 

Perhaps check it again

Member Since 02 Dec 2013
Offline Last Active Today, 07:50 AM
-----

Posts I've Made

In Topic: sorting out a problem

06 March 2014 - 06:47 AM

phil1882,

 

1) The sequence starts off with "2," not "1," because 1 is not a prime number.

 

2) There are commas between the numbers in the sequence and a comma before the ellipsis.

 

3) You are missing the number 18.  18 = 2*3*3  (The number of prime factors is odd.)

 

 

Therefore, the sequence is:

 

2, 3, 5, 7, 8, 11, 12, 13, 17, 18, 19, 20, 23, 27, 28, 29, 30, 31, ...


In Topic: triangle in a circle probability

28 February 2014 - 07:05 AM

"you start off with a circle, and you select 3 points on the circle..."

 

This means you are not choosing any points of the *interior* of the circle.  The likelihood has a probability of zero.

 

The largest triangle area-wise that can be formed with three points chosen *on* the circle is an equilateral one.

And it's area is less than half of the area of the circle.

 

If you want to use the word "on" an object for meaning picking random interior points, you better change the

object to a *disc* instead.  A circle doesn't have any interior points to choose from, but a disc does.

 

That is, if you are told you are selecting points on a circle, then you are not selecting points in the interior

of the circle.


In Topic: Making 271

26 February 2014 - 06:52 AM

bonanova posted:

-------------------------------------------------------------------------------

I would guess "ways" means combinations.

The permutations of 271 1's are not that interesting.

-------------------------------------------------------------------------------

 

I must be a genius when it comes to making arguments, because I would never have typed

that second sentence highlighted above.  It is irrelevant.

When I asked my question, I had already thought through about repetitions of certain numbers.

But your second sentence, bonanova, is irrelevant.  It's on purpose that I try really hard

not to resort to sarcasm with another math forum user when I don't understand why they

stated something that I otherwise would not have stated myself.  And now it should be an

insult for me to point out that the permutations of 271 1's doesn't exclude the possibility of

interesting permutations of other than the sole use of 1's to sum to 271.


In Topic: Factor this

25 February 2014 - 07:23 PM

On one level, that number can be shown to be between one of the numbers 40! and 44!, inclusive.

 

The number in the puzzle written out ends in nine zeroes, so it has exactly none factors of 10.

 

Then it has exactly nine factors of 5.  Start listing consecutive multiples of 5, beginning with 5,

and end until you get to a multiple that contains a cumulative ninth factor of 5:

 

5, 10, 15, 20, 25, 30, 35, 40, 45, 50, ...

 

5, 2*5, 3*5, 4*5, 5*5, 6*5, 7*5, 8*5  ====>  Stop.

 

If you have gone to 45 inclusive, you have gone too far, because that will provide a tenth factor of 5.


In Topic: Making 271

25 February 2014 - 07:02 PM

Is this with regards or without regards to orderings of the summands?