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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
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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
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1000th Post!
PikaPika999   143
N 5 minutes ago by Yihangzh
When I had less than 25 posts on AoPS, I saw many people create threads about them getting 1000th posts. I thought I would never hit 1000 posts, but here we are, this is my 1000th post.

As a lot of users like to do, I'll write my math story:

Daycare
Preschool
Kindergarten
First Grade
Second Grade
Third Grade
Fourth Grade
Fifth Grade
Sixth Grade
Quick Quote that was from MLK that I edited

In conclusion, AoPS has helped me improve my math. I have also made many new friends on AoPS!

Finally, I would like to say thank you to all the new friends I made and all the instructors on AoPS that taught me!

Minor side note, but
143 replies
PikaPika999
Apr 5, 2025
Yihangzh
5 minutes ago
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The daily problem!
Leeoz   112
N 10 minutes ago by huajun78
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!
112 replies
Leeoz
Mar 21, 2025
huajun78
10 minutes ago
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100 post!
JohannIsBach   13
N 37 minutes ago by Dolphincurious79
this is my 100th post! i cant believe it. :wow:
P.S. can everyone who reads this give it an upvote? thx!
13 replies
JohannIsBach
Mar 10, 2025
Dolphincurious79
37 minutes ago
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300 MAP Goal??
Antoinette14   58
N 39 minutes ago by Dolphincurious79
Hey, so as a 6th grader, my big goal for MAP this spring is to get a 300 (ambitious, i know). I'm currently at a 285 (288 last year though). I'm already taking a intro to counting and probability course (One of my weak points), but is there anything else you recommend I focus on to get a 300?
58 replies
Antoinette14
Jan 30, 2025
Dolphincurious79
39 minutes ago
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No more topics!
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Nice Combinatorics Problem
RabtejKalra   10
N Apr 12, 2025 by sadas123
A number is considered happy if it contains at least one digit exactly twice. For instance, the numbers 2020 and 2024 are happy, but the numbers 2019 and 2022 are not. How many happy counting numbers are there that are less than 10,000?
10 replies
RabtejKalra
Apr 11, 2025
sadas123
Apr 12, 2025
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Nice Combinatorics Problem
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RabtejKalra
64 posts
RabtejKalra
#1 h  Apr 11, 2025, 10:16 PM
Y by
A number is considered happy if it contains at least one digit exactly twice. For instance, the numbers 2020 and 2024 are happy, but the numbers 2019 and 2022 are not. How many happy counting numbers are there that are less than 10,000?
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HacheB2031
368 posts
HacheB2031
#2 h  Apr 11, 2025, 10:32 PM
Y by
ez sol
This post has been edited 1 time. Last edited by HacheB2031, Apr 11, 2025, 10:36 PM
Reason: imagine having a computational error wouldnt be me
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Bummer12345
132 posts
Bummer12345
#3 h  Apr 11, 2025, 10:38 PM
Y by
@above there can also be numbers with a digit that repeats more than twice
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HacheB2031
368 posts
HacheB2031
#4 h  Apr 11, 2025, 10:42 PM
Y by
Bummer12345 wrote:
@above there can also be numbers with a digit that repeats more than twice

oops yeah i didn't count $0043$ and stuff let me fix that
HacheB2031 wrote:
idoit sol
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RabtejKalra
64 posts
RabtejKalra
#5 h  Apr 11, 2025, 11:03 PM
Y by
No, 0043 and stuf like that would just be considered 43, so they're sad numbers
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maxamc
551 posts
maxamc
#6 h  Apr 11, 2025, 11:05 PM
Y by
sol
This post has been edited 1 time. Last edited by maxamc, Apr 12, 2025, 12:19 AM
Reason: mistake
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iwastedmyusername
89 posts
iwastedmyusername
#7 h  Apr 12, 2025, 12:00 AM
Y by
maxamc wrote:
sol

You overcounted 243 4 digit numbers (aabb is the same as a permutation of bbaa). So I think the actual answer should be 4626-243=4383
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maxamc
551 posts
maxamc
#8 h  Apr 12, 2025, 12:18 AM
Y by
iwastedmyusername wrote:
maxamc wrote:
sol

You overcounted 243 4 digit numbers (aabb is the same as a permutation of bbaa). So I think the actual answer should be 4626-243=4383

oops, edited my post
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sadas123
1231 posts
sadas123
#9 h  Apr 12, 2025, 2:08 AM
Y by
Bashy 3 minute solution

I took a bit of inspiration from you @maxamc
This post has been edited 2 times. Last edited by sadas123, Apr 12, 2025, 1:23 PM
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maxamc
551 posts
maxamc
#10 h  Apr 12, 2025, 3:21 AM
Y by
sadas123 wrote:
Bashy 3 minute solution

I took a bit of inspiration from you @maxamc

You overcounted 243 4 digit numbers (aabb is the same as a permutation of bbaa). So I think the actual answer should be 4626-243=4383
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sadas123
1231 posts
sadas123
#11 h  Apr 12, 2025, 1:22 PM
Y by
maxamc wrote:
sadas123 wrote:
Bashy 3 minute solution

I took a bit of inspiration from you @maxamc

You overcounted 243 4 digit numbers (aabb is the same as a permutation of bbaa). So I think the actual answer should be 4626-243=4383

oh woops wait I am dumb :( I should have saw that updating my thingie
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