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k a May Highlights and 2025 AoPS Online Class Information
jlacosta   0
May 1, 2025
May is an exciting month! National MATHCOUNTS is the second week of May in Washington D.C. and our Founder, Richard Rusczyk will be presenting a seminar, Preparing Strong Math Students for College and Careers, on May 11th.

Are you interested in working towards MATHCOUNTS and don’t know where to start? We have you covered! If you have taken Prealgebra, then you are ready for MATHCOUNTS/AMC 8 Basics. Already aiming for State or National MATHCOUNTS and harder AMC 8 problems? Then our MATHCOUNTS/AMC 8 Advanced course is for you.

Summer camps are starting next month at the Virtual Campus in math and language arts that are 2 - to 4 - weeks in duration. Spaces are still available - don’t miss your chance to have an enriching summer experience. 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 upcoming events:
[list][*]May 9th, 4:30pm PT/7:30pm ET, Casework 2: Overwhelming Evidence — A Text Adventure, a game where participants will work together to navigate the map, solve puzzles, and win! All are welcome.
[*]May 19th, 4:30pm PT/7:30pm ET, What's Next After Beast Academy?, designed for students finishing Beast Academy and ready for Prealgebra 1.
[*]May 20th, 4:00pm PT/7:00pm ET, Mathcamp 2025 Qualifying Quiz Part 1 Math Jam, Problems 1 to 4, join the Canada/USA Mathcamp staff for this exciting Math Jam, where they discuss solutions to Problems 1 to 4 of the 2025 Mathcamp Qualifying Quiz!
[*]May 21st, 4:00pm PT/7:00pm ET, Mathcamp 2025 Qualifying Quiz Part 2 Math Jam, Problems 5 and 6, Canada/USA Mathcamp staff will discuss solutions to Problems 5 and 6 of the 2025 Mathcamp Qualifying Quiz![/list]
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0 replies
jlacosta
May 1, 2025
0 replies
Hard Number Theory Problem
ZeltaQN2008   0
10 minutes ago
Source: VIMONI Test 2025
Let $n$ be a positive integer. Define $N_1$ as the number of integer pairs $(x,y)$ satisfying $x^{2}+3y^{2}=8n+4$ with $x$ odd. Define $N_2$ as the number of integer pairs $(x,y)$ satisfying $x^{2}+3y^{2}=8n+4.$
Prove that $N_{1}= \frac23\,N_{2}.$

0 replies
ZeltaQN2008
10 minutes ago
0 replies
Hard math inequality
noneofyou34   1
N 12 minutes ago by JARP091
If a,b,c are positive real numbers, such that a+b+c=1. Prove that:
(b+c)(a+c)/(a+b)+ (b+a)(a+c)/(c+b)+(b+c)(a+b)/(a+c)>= Sqrt.(6(a(a+c)+b(a+b)+c(b+c)) +3
1 reply
noneofyou34
an hour ago
JARP091
12 minutes ago
Highest degree for 3-layer power tower (IMO ShortList 1991)
orl   36
N 18 minutes ago by SomeonecoolLovesMaths
Source: IMO ShortList 1991, Problem 18 (BUL 1)
Find the highest degree $ k$ of $ 1991$ for which $ 1991^k$ divides the number \[ 1990^{1991^{1992}} + 1992^{1991^{1990}}.\]
36 replies
orl
Aug 15, 2008
SomeonecoolLovesMaths
18 minutes ago
Consecutive QR
FireBreathers   0
27 minutes ago
Is it true that the longest chain of consecutive quadratic residues in modulo $p$ $\leq 2\sqrt{p}$?
0 replies
FireBreathers
27 minutes ago
0 replies
Max and min of ab+bc+ca-abc
Tiira   5
N 2 hours ago by sqing
a, b and c are three non-negative reel numbers such that a+b+c=1.
What are the extremums of
ab+bc+ca-abc
?
5 replies
Tiira
Jan 29, 2021
sqing
2 hours ago
Inequalities
sqing   12
N 2 hours ago by sqing
Let $a,b,c >2 $ and $ ab+bc+ca \leq 75.$ Show that
$$\frac{1}{a-2}+\frac{1}{b-2}+\frac{1}{c-2}\geq 1$$Let $a,b,c >2 $ and $ \frac{1}{a}+\frac{1}{b}+\frac{1}{c}\geq \frac{6}{7}.$ Show that
$$\frac{1}{a-2}+\frac{1}{b-2}+\frac{1}{c-2}\geq 2$$
12 replies
sqing
May 13, 2025
sqing
2 hours ago
2017 DMI Individual Round - Downtown Mathematics Invitational
parmenides51   14
N 3 hours ago by SomeonecoolLovesMaths
p1. Compute the smallest positive integer $x$ such that $351x$ is a perfect cube.


p2. A four digit integer is chosen at random. What is the probability all $4$ digits are distinct?


p3. If $$\frac{\sqrt{x + 1}}{\sqrt{x}}+ \frac{\sqrt{x}}{\sqrt{x + 1}} =\frac52.$$Solve for $x$.


p4. In $\vartriangle ABC$, $AB = 13$, $BC = 14$, and $AC = 15$. Let $D$ be the point on $BC$ such that $AD \perp BC$, and let $E$ be the midpoint of $AD$. If $F$ is a point such that $CDEF$ is a rectangle, compute the area of $\vartriangle AEF$.


p5. Square $ABCD$ has a sidelength of $4$. Points $P$, $Q$, $R$, and $S$ are chosen on $AB$, $BC$, $CD$, and $AD$ respectively, such that $AP$, $BQ$, $CR$, and $DS$ are length $1$. Compute the area of quadrilateral $P QRS$.


p6. A sequence $a_n$ satisfies for all integers $n$, $$a_{n+1} = 3a_n - 2a_{n-1}.$$If $a_0 = -30$ and $a_1 = -29$, compute $a_{11}$.


p7. In a class, every child has either red hair, blond hair, or black hair. All but $20$ children have black hair, all but $17$ have red hair, and all but $5$ have blond hair. How many children are there in the class?


p8. An Akash set is a set of integers that does not contain two integers such that one divides the other. Compute the minimum positive integer $n$ such that the set $\{1, 2, 3, ..., 2017\}$ can be partitioned into n Akash subsets.


PS. You should use hide for answers. Collected here.
14 replies
parmenides51
Oct 2, 2023
SomeonecoolLovesMaths
3 hours ago
p+2^p-3=n^2
tom-nowy   0
4 hours ago
Let $n$ be a natural number and $p$ be a prime number. How many different pairs $(n, p)$ satisfy the equation:
$$p + 2^p - 3 = n^2 .$$
Inspired by https://artofproblemsolving.com/community/c4h3560823
0 replies
tom-nowy
4 hours ago
0 replies
Range of a function
Pscgylotti   1
N 6 hours ago by Mathzeus1024
Try to get the range of function $f(x)=cosx+\sqrt{cos^{2}x-4\sqrt{2}cosx+4sinx+9}$ :
1 reply
Pscgylotti
Jul 22, 2019
Mathzeus1024
6 hours ago
Inequalities
sqing   17
N 6 hours ago by sqing
Let $ a,b,c>0 , a+b+c +abc=4$. Prove that
$$ \frac {a}{a^2+2}+\frac {b}{b^2+2}+\frac {c}{c^2+2} \leq 1$$Let $ a,b,c>0 , ab+bc+ca+abc=4$. Prove that
$$ \frac {a}{a^2+2}+\frac {b}{b^2+2}+\frac {c}{c^2+2} \leq 1$$
17 replies
sqing
May 15, 2025
sqing
6 hours ago
Calculate the function
Arkham   1
N 6 hours ago by Mathzeus1024
Consider $ y = f (x) = \arcsin (- \sqrt {1 + 10x}) $, $ x \in [-1 / 10,0] $. Calculate the function where $ g $ is the inverse function of $ f $

Note: $ g (y) = f ^ {- 1} (y) $]
1 reply
Arkham
Apr 29, 2021
Mathzeus1024
6 hours ago
Ez comb proposed by ME
IEatProblemsForBreakfast   0
6 hours ago
A and B play a game on two table:
1.At first one table got $n$ different coloured marbles on it and another one is empty
2.At each move player choose set of marbles that hadn't choose either players before and all chosen marbles from same table, and move all the marbles in that set to another table
3.Player who can not move lose
If A starts and they move alternatily who got the winning strategy?
0 replies
IEatProblemsForBreakfast
6 hours ago
0 replies
Incircle concurrency
niwobin   3
N Today at 8:37 AM by sunken rock
Triangle ABC with incenter I, incircle is tangent to BC, AC, and AB at D, E and F respectively.
DT is a diameter for the incircle, and AT meets the incircle again at point H.
Let DH and EF intersect at point J. Prove: AJ//BC.
3 replies
niwobin
May 11, 2025
sunken rock
Today at 8:37 AM
Combination
AnhIsGod   1
N Today at 7:47 AM by alexheinis
A group consists of 21 people. A and B are said to have a "known relationship" if A knows B or A knows C_1, C_1 knows C_2, ..., C_n knows B. It is known that among any 6 people, there are always 2 who have a known relationship. Prove that in this group, there always exists a group of 5 people who all have a "known relationship" with each other.
1 reply
AnhIsGod
Today at 7:29 AM
alexheinis
Today at 7:47 AM
Abstraction function in combinatorics
Assassino9931   0
Apr 27, 2025
Source: Balkan MO Shortlist 2024 C2
Let $n\geq 2$ be an integer and denote $S = \{1,2,\ldots,n^2\}$. For a function $f: S \to S$ we denote Im $f = \{b\in S: \exists a\in S, f(a) = b\}$, Fix $f = \{x \in S: f(x) = x\}$ and $f^{-1}(k) = \{a\in S: f(a) = k\}$. Find all possible values of $|$Im $f|$ + $|$Fix $f|$ + $\max_{k\in S} |f^{-1}(k)|$.
0 replies
Assassino9931
Apr 27, 2025
0 replies
Abstraction function in combinatorics
G H J
Source: Balkan MO Shortlist 2024 C2
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Assassino9931
1356 posts
#1
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Let $n\geq 2$ be an integer and denote $S = \{1,2,\ldots,n^2\}$. For a function $f: S \to S$ we denote Im $f = \{b\in S: \exists a\in S, f(a) = b\}$, Fix $f = \{x \in S: f(x) = x\}$ and $f^{-1}(k) = \{a\in S: f(a) = k\}$. Find all possible values of $|$Im $f|$ + $|$Fix $f|$ + $\max_{k\in S} |f^{-1}(k)|$.
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