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k a April Highlights and 2025 AoPS Online Class Information
jlacosta   0
Apr 2, 2025
Spring is in full swing and summer is right around the corner, what are your plans? At AoPS Online our schedule has new classes starting now through July, so be sure to keep your skills sharp and be prepared for the Fall school year! Check out the schedule of upcoming classes below.

WOOT early bird pricing is in effect, don’t miss out! If you took MathWOOT Level 2 last year, no worries, it is all new problems this year! Our Worldwide Online Olympiad Training program is for high school level competitors. AoPS designed these courses to help our top students get the deep focus they need to succeed in their specific competition goals. Check out the details at this link for all our WOOT programs in math, computer science, chemistry, and physics.

Looking for summer camps in math and language arts? Be sure to check out the video-based summer camps offered at the Virtual Campus that are 2- to 4-weeks in duration. There are middle and high school competition math camps as well as Math Beasts camps that review key topics coupled with fun explorations covering areas such as graph theory (Math Beasts Camp 6), cryptography (Math Beasts Camp 7-8), and topology (Math Beasts Camp 8-9)!

Be sure to mark your calendars for the following events:
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April 9th (Webinar), 4:00pm PT/7:00pm ET, Learn about Video-based Summer Camps at the Virtual Campus
[*]April 10th (Math Jam), 4:30pm PT/7:30pm ET, 2025 MathILy and MathILy-Er Math Jam: Multibackwards Numbers
[*]April 22nd (Webinar), 4:00pm PT/7:00pm ET, Competitive Programming at AoPS (USACO).[/list]
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0 replies
jlacosta
Apr 2, 2025
0 replies
k i Adding contests to the Contest Collections
dcouchman   1
N Apr 5, 2023 by v_Enhance
Want to help AoPS remain a valuable Olympiad resource? Help us add contests to AoPS's Contest Collections.

Find instructions and a list of contests to add here: https://artofproblemsolving.com/community/c40244h1064480_contests_to_add
1 reply
dcouchman
Sep 9, 2019
v_Enhance
Apr 5, 2023
k i Zero tolerance
ZetaX   49
N May 4, 2019 by NoDealsHere
Source: Use your common sense! (enough is enough)
Some users don't want to learn, some other simply ignore advises.
But please follow the following guideline:


To make it short: ALWAYS USE YOUR COMMON SENSE IF POSTING!
If you don't have common sense, don't post.


More specifically:

For new threads:


a) Good, meaningful title:
The title has to say what the problem is about in best way possible.
If that title occured already, it's definitely bad. And contest names aren't good either.
That's in fact a requirement for being able to search old problems.

Examples:
Bad titles:
- "Hard"/"Medium"/"Easy" (if you find it so cool how hard/easy it is, tell it in the post and use a title that tells us the problem)
- "Number Theory" (hey guy, guess why this forum's named that way¿ and is it the only such problem on earth¿)
- "Fibonacci" (there are millions of Fibonacci problems out there, all posted and named the same...)
- "Chinese TST 2003" (does this say anything about the problem¿)
Good titles:
- "On divisors of a³+2b³+4c³-6abc"
- "Number of solutions to x²+y²=6z²"
- "Fibonacci numbers are never squares"


b) Use search function:
Before posting a "new" problem spend at least two, better five, minutes to look if this problem was posted before. If it was, don't repost it. If you have anything important to say on topic, post it in one of the older threads.
If the thread is locked cause of this, use search function.

Update (by Amir Hossein). The best way to search for two keywords in AoPS is to input
[code]+"first keyword" +"second keyword"[/code]
so that any post containing both strings "first word" and "second form".


c) Good problem statement:
Some recent really bad post was:
[quote]$lim_{n\to 1}^{+\infty}\frac{1}{n}-lnn$[/quote]
It contains no question and no answer.
If you do this, too, you are on the best way to get your thread deleted. Write everything clearly, define where your variables come from (and define the "natural" numbers if used). Additionally read your post at least twice before submitting. After you sent it, read it again and use the Edit-Button if necessary to correct errors.


For answers to already existing threads:


d) Of any interest and with content:
Don't post things that are more trivial than completely obvious. For example, if the question is to solve $x^{3}+y^{3}=z^{3}$, do not answer with "$x=y=z=0$ is a solution" only. Either you post any kind of proof or at least something unexpected (like "$x=1337, y=481, z=42$ is the smallest solution). Someone that does not see that $x=y=z=0$ is a solution of the above without your post is completely wrong here, this is an IMO-level forum.
Similar, posting "I have solved this problem" but not posting anything else is not welcome; it even looks that you just want to show off what a genius you are.

e) Well written and checked answers:
Like c) for new threads, check your solutions at least twice for mistakes. And after sending, read it again and use the Edit-Button if necessary to correct errors.



To repeat it: ALWAYS USE YOUR COMMON SENSE IF POSTING!


Everything definitely out of range of common sense will be locked or deleted (exept for new users having less than about 42 posts, they are newbies and need/get some time to learn).

The above rules will be applied from next monday (5. march of 2007).
Feel free to discuss on this here.
49 replies
ZetaX
Feb 27, 2007
NoDealsHere
May 4, 2019
D1025 : Can you do that?
Dattier   3
N an hour ago by Dattier
Source: les dattes à Dattier
Let $x_{n+1}=x_n^3$ and $x_0=3$.

Can you calculate $\sum\limits_{i=1}^{2^{2025}} x_i \mod 10^{30}$?
3 replies
Dattier
Yesterday at 8:24 PM
Dattier
an hour ago
Parallel condition and isogonal
ItzsleepyXD   1
N an hour ago by moony_
Source: Own , Mock Thailand Mathematic Olympiad P5
Let $ABC$ be triangle and point $D$ be $A-$ altitude of $\triangle ABC$ .
Let $E,F$ be a point on $AC$ and $AB$ such that $DE\parallel AB$ and $DF\parallel AC$ . Point $G$ is the intersection of $(AEF)$ and $(ABC)$ . Point $P$ be intersection of $(ADG)$ and $BC$ . Line $GD$ intersect circumcircle of $\triangle ABC$ again at $Q$ .
Prove that
(a) $\angle BAP = \angle QAC$ .
(b) $AQ$ bisect $BC$ .
1 reply
ItzsleepyXD
2 hours ago
moony_
an hour ago
RMM 2013 Problem 1
dr_Civot   31
N an hour ago by cursed_tangent1434
For a positive integer $a$, define a sequence of integers $x_1,x_2,\ldots$ by letting $x_1=a$ and $x_{n+1}=2x_n+1$ for $n\geq 1$. Let $y_n=2^{x_n}-1$. Determine the largest possible $k$ such that, for some positive integer $a$, the numbers $y_1,\ldots,y_k$ are all prime.
31 replies
dr_Civot
Mar 2, 2013
cursed_tangent1434
an hour ago
Inspired by old results
sqing   0
an hour ago
Source: Own
Let $  a , b , c>0  $and $  abc=1 $. Prove that
$$\frac{a^2}{b}+\frac{b^2}{c}+\frac{c^2}{a} +3 \geq  \frac{a}{b}+\frac{b}{c}+\frac{c}{a}+\frac{1}{a}+\frac{1}{b}+\frac{1}{c}$$h
0 replies
sqing
an hour ago
0 replies
amazing balkan combi
egxa   7
N an hour ago by Assassino9931
Source: BMO 2025 P4
There are $n$ cities in a country, where $n \geq 100$ is an integer. Some pairs of cities are connected by direct (two-way) flights. For two cities $A$ and $B$ we define:

$(i)$ A $\emph{path}$ between $A$ and $B$ as a sequence of distinct cities $A = C_0, C_1, \dots, C_k, C_{k+1} = B$, $k \geq 0$, such that there are direct flights between $C_i$ and $C_{i+1}$ for every $0 \leq i \leq k$;
$(ii)$ A $\emph{long path}$ between $A$ and $B$ as a path between $A$ and $B$ such that no other path between $A$ and $B$ has more cities;
$(iii)$ A $\emph{short path}$ between $A$ and $B$ as a path between $A$ and $B$ such that no other path between $A$ and $B$ has fewer cities.
Assume that for any pair of cities $A$ and $B$ in the country, there exist a long path and a short path between them that have no cities in common (except $A$ and $B$). Let $F$ be the total number of pairs of cities in the country that are connected by direct flights. In terms of $n$, find all possible values $F$

Proposed by David-Andrei Anghel, Romania.
7 replies
2 viewing
egxa
Apr 27, 2025
Assassino9931
an hour ago
Question on Balkan SL
Fmimch   2
N an hour ago by Assassino9931
Does anyone know where to find the Balkan MO Shortlist 2024? If you have the file, could you send in this thread? Thank you!
2 replies
Fmimch
Today at 12:13 AM
Assassino9931
an hour ago
Or statement function
ItzsleepyXD   1
N an hour ago by Haris1
Source: Own , Mock Thailand Mathematic Olympiad P2
Find all $f: \mathbb{R} \to \mathbb{Z^+}$ such that $$f(x+f(y))=f(x)+f(y)+1\quad\text{ or }\quad f(x)+f(y)-1$$for all real number $x$ and $y$
1 reply
ItzsleepyXD
2 hours ago
Haris1
an hour ago
Add a digit to obtain a new perfect square
Lukaluce   2
N an hour ago by TopGbulliedU
Source: 2024 Junior Macedonian Mathematical Olympiad P4
Let $a_1, a_2, ..., a_n$ be a sequence of perfect squares such that $a_{i + 1}$ can be obtained by concatenating a digit to the right of $a_i$. Determine all such sequences that are of maximum length.

Proposed by Ilija Jovčeski
2 replies
Lukaluce
Apr 14, 2025
TopGbulliedU
an hour ago
Simple inequality
sqing   7
N 2 hours ago by sqing
Source: Daniel Sitaru
Let $a,b,c>0$ . Prove that$$\frac{a^3}{b^3}+\frac{b^3}{c^3}+\frac{c^3}{a^3}+9>\frac{3}{2}\left(\frac{a^2}{b^2}+\frac{b^2}{c^2}+\frac{c^2}{a^2}+
\frac{a}{b}+\frac{b}{c}+\frac{c}{a}\right)$$
7 replies
sqing
Feb 10, 2017
sqing
2 hours ago
Vector Vortex
steven_zhang123   1
N 2 hours ago by Mathzeus1024
Source: NS Issue 1 P3 (2014.4)
Let $v_{1}, v_{2}, \cdots, v_{n}$ be $n$ unit vectors on a plane, where $n$ is an odd number. Prove that there exist $\varepsilon _i\in \left \{ -1,1 \right \} $ for $i=1,2,\cdots,n$ such that $\left | \sum_{i=1}^{n} \varepsilon_i v_i \right | \le 1.$
1 reply
steven_zhang123
Feb 15, 2025
Mathzeus1024
2 hours ago
Website to learn math
hawa   71
N 2 hours ago by Chonkachu
Hi, I'm kinda curious what website do yall use to learn math, like i dont find any website thats fun to learn math
71 replies
hawa
Apr 9, 2025
Chonkachu
2 hours ago
The daily problem!
Leeoz   155
N 5 hours ago by elizhang101412
Every day, I will try to post a new problem for you all to solve! If you want to post a daily problem, you can! :)

Please hide solutions and answers, hints are fine though! :)

Problems usually get harder throughout the week, so Sunday is the easiest and Saturday is the hardest!

Past Problems!
155 replies
Leeoz
Mar 21, 2025
elizhang101412
5 hours ago
9 AMC 8 Scores
ChromeRaptor777   117
N Today at 4:08 AM by valisaxieamc
As far as I'm certain, I think all AMC8 scores are already out. Vote above.
117 replies
ChromeRaptor777
Apr 1, 2022
valisaxieamc
Today at 4:08 AM
Can someone explain this one
hawa   10
N Yesterday at 8:23 PM by VivaanKam
Suppose n is the largest integer obtained by solving the following inequality:

3+9+18+30+...+n
n < 2021.
10 replies
hawa
Yesterday at 1:36 AM
VivaanKam
Yesterday at 8:23 PM
Hello friends
bibidi_skibidi   9
N Apr 16, 2025 by giratina3
Now unfortunately I don't know the difficulty of the problems posted here but I'll try to replicate:

Bob has 20 apples and 19 oranges. How many ways can he split the fruits between 7 people if each person must have at least 1 apple and 2 oranges?

After looking at the other posters I realized just how bashy this is

Also I can only edit this message for now since new AoPS users can only send 6 messages every day
9 replies
bibidi_skibidi
Apr 15, 2025
giratina3
Apr 16, 2025
Hello friends
G H J
G H BBookmark kLocked kLocked NReply
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bibidi_skibidi
5 posts
#1 • 2 Y
Y by aidan0626, GodGodGodGodGoose
Now unfortunately I don't know the difficulty of the problems posted here but I'll try to replicate:

Bob has 20 apples and 19 oranges. How many ways can he split the fruits between 7 people if each person must have at least 1 apple and 2 oranges?

After looking at the other posters I realized just how bashy this is

Also I can only edit this message for now since new AoPS users can only send 6 messages every day
This post has been edited 1 time. Last edited by bibidi_skibidi, Apr 15, 2025, 4:19 AM
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aidan0626
1876 posts
#2
Y by
Hi :)
This is standard stars and bars, there are $\binom{19}{6}$ ways to split the apples and $\binom{11}{6}$ ways to split the oranges, and you just multiply those two together to get the final answer.
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Soupboy0
344 posts
#3
Y by
bro i got sniped :rotfl:
Z K Y
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maxamc
568 posts
#4
Y by
aidan0626 wrote:
Hi :)
This is standard stars and bars, there are $\binom{19}{6}$ ways to split the apples and $\binom{11}{6}$ ways to split the oranges, and you just multiply those two together to get the final answer.

Wolfram Alpha gives 12534984 as our final answer (impossible to compute)
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fluffyyyyyyy
1 post
#5
Y by
hello sabko
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Leeoz
178 posts
#6
Y by
maxamc wrote:
aidan0626 wrote:
Hi :)
This is standard stars and bars, there are $\binom{19}{6}$ ways to split the apples and $\binom{11}{6}$ ways to split the oranges, and you just multiply those two together to get the final answer.

Wolfram Alpha gives 12534984 as our final answer (impossible to compute)

its not "impossible" :P
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Thayaden
1361 posts
#7
Y by
bibidi_skibidi wrote:
Now unfortunately I don't know the difficulty of the problems posted here but I'll try to replicate:

Bob has 20 apples and 19 oranges. How many ways can he split the fruits between 7 people if each person must have at least 1 apple and 2 oranges?

After looking at the other posters I realized just how bashy this is

Also I can only edit this message for now since new AoPS users can only send 6 messages every day

Start by giving away the required fruit this leaves 18 fruit for grabs namely 13 ap0pels and 5 oranges we set up stars and bars for extras and get (13+6)! but yet no oranges is diffrent from another orange and there are 5! ways to arage oranges and 13! ways to arange appels and 6! ways to arange bars so I think our answer is $\boxed{\frac{(18+6)!}{5!13!6!}}$ is what I got
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maxamc
568 posts
#8
Y by
Thayaden wrote:
bibidi_skibidi wrote:
Now unfortunately I don't know the difficulty of the problems posted here but I'll try to replicate:

Bob has 20 apples and 19 oranges. How many ways can he split the fruits between 7 people if each person must have at least 1 apple and 2 oranges?

After looking at the other posters I realized just how bashy this is

Also I can only edit this message for now since new AoPS users can only send 6 messages every day

Start by giving away the required fruit this leaves 18 fruit for grabs namely 13 ap0pels and 5 oranges we set up stars and bars for extras and get (13+6)! but yet no oranges is diffrent from another orange and there are 5! ways to arage oranges and 13! ways to arange appels and 6! ways to arange bars so I think our answer is $\boxed{\frac{(18+6)!}{5!13!6!}}$ is what I got

Your answer is 1153218528, not equal to my Wolfram Alpha answer described above, unfortunately wrong I think.
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BS2012
1025 posts
#9
Y by
its just Solution sketch which is the same as the 2nd post
This post has been edited 3 times. Last edited by BS2012, Apr 16, 2025, 12:52 AM
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giratina3
495 posts
#10
Y by
This is not bashy at all if you know Stars and Bars. I would recommend reading the later sections of Intro to Counting and Probability for more information.
This post has been edited 1 time. Last edited by giratina3, Apr 16, 2025, 2:57 AM
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