Stay ahead of learning milestones! Enroll in a class over the summer!

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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:
[list][*]April 3rd (Webinar), 4pm PT/7:00pm ET, Learning with AoPS: Perspectives from a Parent, Math Camp Instructor, and University Professor
[*]April 8th (Math Jam), 4:30pm PT/7:30pm ET, 2025 MATHCOUNTS State Discussion
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]
Our full course list for upcoming classes is below:
All classes run 7:30pm-8:45pm ET/4:30pm - 5:45pm PT unless otherwise noted.

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0 replies
jlacosta
Apr 2, 2025
0 replies
Sequence with condition on million consecutive terms
jbaca   13
N 9 minutes ago by Ilikeminecraft
Source: 2021 Iberoamerican Mathematical Olympiad, P3
Let $a_1,a_2,a_3, \ldots$ be a sequence of positive integers and let $b_1,b_2,b_3,\ldots$ be the sequence of real numbers given by
$$b_n = \dfrac{a_1a_2\cdots a_n}{a_1+a_2+\cdots + a_n},\ \mbox{for}\ n\geq 1$$Show that, if there exists at least one term among every million consecutive terms of the sequence $b_1,b_2,b_3,\ldots$ that is an integer, then there exists some $k$ such that $b_k > 2021^{2021}$.
13 replies
jbaca
Oct 20, 2021
Ilikeminecraft
9 minutes ago
Operations on Pebbles
MarkBcc168   24
N 15 minutes ago by EeEeRUT
Source: ISL 2022 C6
Let $n$ be a positive integer. We start with $n$ piles of pebbles, each initially containing a single pebble. One can perform moves of the following form: choose two piles, take an equal number of pebbles from each pile and form a new pile out of these pebbles. Find (in terms of $n$) the smallest number of nonempty piles that one can obtain by performing a finite sequence of moves of this form.
24 replies
MarkBcc168
Jul 9, 2023
EeEeRUT
15 minutes ago
Dou Fang Geometry in Taiwan TST
Li4   0
22 minutes ago
Source: 2025 Taiwan TST Round 3 Mock P2
Let $\omega$ and $\Omega$ be the incircle and circumcircle of the acute triangle $ABC$, respectively. Draw a square $WXYZ$ so that all of its sides are tangent to $\omega$, and $X$, $Y$ are both on $BC$. Extend $AW$ and $AZ$, intersecting $\Omega$ at $P$ and $Q$, respectively. Prove that $PX$ and $QY$ intersects on $\Omega$.

Proposed by kyou46, Li4, Revolilol.
0 replies
Li4
22 minutes ago
0 replies
[EGMO3] GCD Bounds
socrates   18
N 43 minutes ago by Ilikeminecraft
Source: EGMO 2015, Problem 3
Let $n, m$ be integers greater than $1$, and let $a_1, a_2, \dots, a_m$ be positive integers not greater than $n^m$. Prove that there exist positive integers $b_1, b_2, \dots, b_m$ not greater than $n$, such that \[ \gcd(a_1 + b_1, a_2 + b_2, \dots, a_m + b_m) < n, \] where $\gcd(x_1, x_2, \dots, x_m)$ denotes the greatest common divisor of $x_1, x_2, \dots, x_m$.
18 replies
socrates
Apr 16, 2015
Ilikeminecraft
43 minutes ago
No more topics!
Ant wanna come to A
Rohit-2006   3
N Apr 16, 2025 by Rohit-2006
An insect starts from $A$ and in $10$ steps and has to reach $A$ again. But in between one of the s steps and can't go $A$. Find probability. For example $ABCDCDEDEA$ is valid but $ABABCDEABA$ is not valid.

*Too many edits, my brain had gone to a trip
3 replies
Rohit-2006
Apr 15, 2025
Rohit-2006
Apr 16, 2025
Ant wanna come to A
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Rohit-2006
227 posts
#1 • 1 Y
Y by cubres
An insect starts from $A$ and in $10$ steps and has to reach $A$ again. But in between one of the s steps and can't go $A$. Find probability. For example $ABCDCDEDEA$ is valid but $ABABCDEABA$ is not valid.

*Too many edits, my brain had gone to a trip
Attachments:
This post has been edited 4 times. Last edited by Rohit-2006, Apr 16, 2025, 2:23 AM
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Rohit-2006
227 posts
#2
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Yaaay my 200th post
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zhaoli
418 posts
#3
Y by
Not clear about "in between one of the s steps and can't go A". What is the difference between the two examples?
Z K Y
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Rohit-2006
227 posts
#4
Y by
zhaoli wrote:
Not clear about "in between one of the s steps and can't go A". What is the difference between the two examples?

Edited, sorry,...one string has no A in between the first and last A, but the second string has
This post has been edited 1 time. Last edited by Rohit-2006, Apr 16, 2025, 2:24 AM
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