Classic graph theory lemma?
by eulerleonhardfan, Apr 24, 2025, 1:29 PM







Inspired by 2024 Fall LMT Guts
by sqing, Apr 24, 2025, 12:24 PM
Let
,
,
are pairwise distinct real numbers satisfying
Prove that
Let
,
,
are pairwise distinct real numbers satisfying
Prove that











This post has been edited 2 times. Last edited by sqing, 2 hours ago
Why is the old one deleted?
by EeEeRUT, Apr 16, 2025, 1:33 AM
For a positive integer
, let
be all positive integers smaller than
that are coprime to
. Find all
such that
for all 
Here
is the largest positive integer that divides both
and
. Integers
and
are coprime if
.
Proposed by Paulius Aleknavičius, Lithuania







Here






Proposed by Paulius Aleknavičius, Lithuania
This post has been edited 2 times. Last edited by EeEeRUT, Apr 18, 2025, 12:56 AM
Reason: Authorship
Reason: Authorship
Dividing Pairs
by Jackson0423, Apr 13, 2025, 8:39 AM
Let
and
be positive integers.
Suppose that
is a divisor of
and
is a divisor of
.
Find all such pairs
.


Suppose that




Find all such pairs

circle geometry showing perpendicularity
by Kyj9981, Mar 18, 2025, 11:53 AM
Two circles
and
intersect at points
and
. A line through
intersects
and
at points
and
, respectively. Line
intersects
at point
, and line
intersects
at point
. If
is the circumcenter of
, prove that
.


















3 knightlike moves is enough
by sarjinius, Mar 9, 2025, 3:38 PM
An ant is on the Cartesian plane. In a single move, the ant selects a positive integer
, then either travels
, the ant can choose to go to one of eight possible points.
Prove that, for any integers
and
, the ant can travel from
to
using at most
moves.

units vertically (up or down) and
units horizontally (left or right); or
units horizontally (left or right) and
units vertically (up or down).

Prove that, for any integers





Min Number of Subsets of Strictly Increasing
by taptya17, Dec 13, 2024, 8:24 AM
Let
be a positive integer. Initially the sequence
(
times) is written on the board. In each round, Ananya choses an integer
and a subset of the numbers written on the board and adds
to all of them. What is the minimum number of rounds in which Ananya can make the sequence on the board strictly increasing?
Proposed by Shantanu Nene





Proposed by Shantanu Nene
Nice inequality
by sqing, Apr 24, 2019, 1:01 PM
Let
be real numbers . Prove that : There exist positive integer
such that
Where 




Combinatorics #2
by utkarshgupta, Feb 18, 2017, 10:46 AM
Problem (ISL 2004 C5) :
and
play a game, given an integer
,
writes down
first, then every player sees the last number written and if it is
then in his turn he writes
or
, but his number cannot be bigger than
. The player who writes
wins. For which values of
does
win?
Proposed by A. Slinko & S. Marshall, New Zealand
Idea of Solution












Proposed by A. Slinko & S. Marshall, New Zealand
Idea of Solution
The questions is kinda easy if you dont know the answer
.
Well I will be only instructive !
Show that
will win for all odd
.
And then show that if
wins for
, she also wins for
and
.
It's really that simple (as the strategy is realllly easy)
But the answer !
Ohh the answer !
B has a winning strategy for all numbers with it's digits as
in expression of
in base-
.
I couldn't really frame the answer in this way.
But elegant and amazing indeed

Well I will be only instructive !
Show that


And then show that if




It's really that simple (as the strategy is realllly easy)
But the answer !
Ohh the answer !
B has a winning strategy for all numbers with it's digits as



I couldn't really frame the answer in this way.
But elegant and amazing indeed
IMO Shortlist 2014 N6
by hajimbrak, Jul 11, 2015, 9:13 AM
Let
be pairwise coprime positive integers with
being prime and
. On the segment
of the real line, mark all integers that are divisible by at least one of the numbers
. These points split
into a number of smaller segments. Prove that the sum of the squares of the lengths of these segments is divisible by
.
Proposed by Serbia



![$I = [0, a_1 a_2 \cdots a_n ]$](http://latex.artofproblemsolving.com/a/2/b/a2bce96b048c9b8fc94926db80aba37fd5037b4a.png)



Proposed by Serbia
This post has been edited 2 times. Last edited by hajimbrak, Jul 23, 2015, 10:52 AM
Reason: Added proposer
Reason: Added proposer
Stay insane,Coz it's your will, labour and pain,which takes you to the top of the mountain.
Archives

















Shouts
Submit
48 shouts
Contributors
Tags
About Owner
- Posts: 2280
- Joined: Jan 4, 2013
Blog Stats
- Blog created: Nov 30, 2013
- Total entries: 86
- Total visits: 39802
- Total comments: 102
Search Blog