All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Numbers
Make it equal (Posted on 2010-05-26) Difficulty: 4 of 5
Divide the set {1,2,3,4, ....,n} into three disjoint subsets A , B , C whose sums of elements are equal. For what values of n it is feasible?

See The Solution Submitted by Ady TZIDON    
Rating: 3.0000 (2 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
half of it | Comment 1 of 7
I am assuming that the union of A,B,C must be {1,2,3,...,n}
a method for even n immediately comes to mind
let n be even
then we can break the set down into n/2 groups of two as such
{1,n}
{2,n-1}
{3,n-2}
....
{n/2,(n+2)/2}
all of which have the equal sum of n+1
so now all we need is for there to be at least three of these, thus n/2>=3 or n>=6
and we can simply construct A,B, and C from these groupings by placing each of them into one of the three sets.

For even numbers n<6 we have n=2 and n=4
if n=2 then we obviously don't have enough elements for three disjoint subsets
if n=4 then it is equally impossible to form such a set.

Thus it is possible to form A,B, and C for all even n>=6

what remains is to determine criteria for odd n

  Posted by Daniel on 2010-05-26 16:52:29
Please log in:
Login:
Password:
Remember me:
Sign up! | Forgot password


Search:
Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (14)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2024 by Animus Pactum Consulting. All rights reserved. Privacy Information