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Modular Arithmetic Handout
MathCosine   16
N 2 hours ago by MathCosine
Hi everyone,

I recently created a handout on modular arithmetic for a local math club. I thought it would help quite a lot with understanding basic properties, as modular arithmetic is a very popular intermediate step in number theory problems, so I decided to leave it here as a resource for anyone who needs it. Feel free to share it around, and hope it helps!

Sincerely,
MathCosine
16 replies
MathCosine
Apr 7, 2025
MathCosine
2 hours ago
idk12345678 Math Contest
idk12345678   0
2 hours ago
Welcome to the 1st idk12345678 Math Contest.
You have 4 hours. You do not have to prove your answers.
Post your answers in a hide tag and I will tell you your score.*


The contest is attached to the post

Clarifications


*I mightve done them wrong feel free to ask about an answer
0 replies
idk12345678
2 hours ago
0 replies
How to get good at comp math
fossasor   9
N 3 hours ago by Inaaya
I'm a rising ninth grader who wasn't in the school math league this year, and basically put aside comp math for a year. Unfortunately, that means that now that I'm in high school and having the epiphany about how important comp math actually is, and how much it would help my chances of getting involved in other math-related programs. In addition, I do enjoy math in general, and suspect that things like the AMCs are probably going to be some of the best practice I can get. What this all means is that I'm trying to go from mediocre to orz, 2 years after I probably should have started if I wanted to be any good.

So my question is: how do I get good at comp math?

This year, my scores on AMC 10 (and these are the highest I've ever gotten) were a 73.5 and an 82.5 (AMC 8 was 21/25, but that doesn't matter much). This is not good enough to qualify for AIME, and I probably need to raise my performance on each by at least 10 points. I've been decently good in the past at Number Theory, but I need to work on Geo and Combinatorics, and I'm trying to find the best resources to do that. My biggest flaw is probably not knowing many algorithms like Stars and Bars, and the path is clear here (learn them) but I'm still not sure which ones I need to know.

I'm aware that some of this advice is going to be something like "Practice 5 hours a day and start hardgrinding" or something along those lines. Unfortunately, I have other extracurriculars I need to balance, and for me, time is a limiting resource. My parents are somewhat frowning upon me doing a lot of comp math, which limits my time as well. I have neither the time nor motivation to do more than an hour a day, and in practice, I don't think I can be doing that consistently. As such, I would need to make that time count.

I know this is a very general question, and that aops is chock-full of detailed advice for math competitions. However, I'd appreciate it if anyone here could help me out, or show me the best resources I should use to get started. What mocks are any good, or what textbooks should I use? Where do I get the best practice with the shortest time? Is there some place I can find a list of useful formulas that have appeared in math comps before?

All advice is welcome!

9 replies
fossasor
5 hours ago
Inaaya
3 hours ago
1990 AMC 12 #24
dft   17
N 3 hours ago by Bread10
All students at Adams High School and at Baker High School take a certain exam. The average scores for boys, for girls, and for boys and girls combined, at Adams HS and Baker HS are shown in the table, as is the average for boys at the two schools combined. What is the average score for the girls at the two schools combined?
\[ \begin{tabular}{c c c c} 
{} & \textbf{Adams} & \textbf{Baker} & \textbf{Adams and Baker}  \\
\textbf{Boys:} & 71 & 81 & 79   \\
\textbf{Girls:} & 76 & 90 & ?   \\
\textbf{Boys and Girls:} & 74 & 84 &   \\
\end{tabular}
 \]
$ \textbf{(A)}\ 81 \qquad\textbf{(B)}\ 82 \qquad\textbf{(C)}\ 83 \qquad\textbf{(D)}\ 84 \quad\textbf{(E)}\ 85 $
17 replies
dft
Dec 31, 2011
Bread10
3 hours ago
2025 Math and AI 4 Girls Competition: Win Up To $1,000!!!
audio-on   35
N 4 hours ago by Lightybird
Join the 2025 Math and AI 4 Girls Competition for a chance to win up to $1,000!

Hey Everyone, I'm pleased to announce the dates for the 2025 MA4G Competition are set!
Applications will open on March 22nd, 2025, and they will close on April 26th, 2025 (@ 11:59pm PST).

Applicants will have one month to fill out an application with prizes for the top 50 contestants & cash prizes for the top 20 contestants (including $1,000 for the winner!). More details below!

Eligibility:
The competition is free to enter, and open to middle school female students living in the US (5th-8th grade).
Award recipients are selected based on their aptitude, activities and aspirations in STEM.

Event dates:
Applications will open on March 22nd, 2025, and they will close on April 26th, 2025 (by 11:59pm PST)
Winners will be announced on June 28, 2025 during an online award ceremony.

Application requirements:
Complete a 12 question problem set on math and computer science/AI related topics
Write 2 short essays

Prizes:
1st place: $1,000 Cash prize
2nd place: $500 Cash prize
3rd place: $300 Cash prize
4th-10th: $100 Cash prize each
11th-20th: $50 Cash prize each
Top 50 contestants: Over $50 worth of gadgets and stationary


Many thanks to our current and past sponsors and partners: Hudson River Trading, MATHCOUNTS, Hewlett Packard Enterprise, Automation Anywhere, JP Morgan Chase, D.E. Shaw, and AI4ALL.

Math and AI 4 Girls is a nonprofit organization aiming to encourage young girls to develop an interest in math and AI by taking part in STEM competitions and activities at an early age. The organization will be hosting an inaugural Math and AI 4 Girls competition to identify talent and encourage long-term planning of academic and career goals in STEM.

Contact:
mathandAI4girls@yahoo.com

For more information on the competition:
https://www.mathandai4girls.org/math-and-ai-4-girls-competition

More information on how to register will be posted on the website. If you have any questions, please ask here!


35 replies
audio-on
Jan 26, 2025
Lightybird
4 hours ago
amc 10 cooked
PaperMath   118
N 5 hours ago by parnikap
Guys any tips to staying calm? (please don't reply with take a deep breath)
118 replies
1 viewing
PaperMath
Nov 5, 2024
parnikap
5 hours ago
9 Practice AIME Exam
Melissa.   17
N 5 hours ago by fake123
(This practice test is designed to be slightly harder than the real test. I would recommend you take this like a real test, using a 3 hour time limit and no calculator.)

Let me know any suggestions for improvement on test quality, difficulty, problem selection, problem placement, test topics, etc. for the next tests that I make!

Practice AIME

1.
Positive integers a, b, and c satisfy a + b + c = 49 and ab + bc + ca = 471. Find the value of the product abc.

2.
Find the integer closest to the value of (69^(1/2) + 420^(1/2))^2.

3.
Let G and A be two points that are 243 units apart. Suppose A_1 is at G, and for n > 1, A_n is the point on line GA such that A_nA_(n-1) = 243, and A_n is farther from A than G. Let L be the locus of points T such that GT + A_6T = 2025. Find the maximum possible distance from T to line GA as T varies across L.

4.
Find the value of (69 + 12 * 33^(1/2))^(1/2) + (69 - 12 * 33^(1/2))^(1/2).

5.
Find the sum of the numerator and denominator of the probability that two (not necessarily distinct) randomly chosen positive integer divisors of 900 are relatively prime, when expressed as a fraction in lowest terms.

6.
Find the limit of (1x^2 + 345x^6)/(5x^6 + 78x + 90) as x approaches infinity.

7.
Find the slope of the line tangent to the graph of y = 6x^2 + 9x + 420 at the point where y = 615 and x is positive.

8.
Find the smallest positive integer n such that the sum of the positive integer divisors of n is 1344.

9.
Find the first 3 digits after the decimal point in the decimal expansion of the square root of 911.

10.
Let n be the smallest positive integer in base 10 such that the base 2 expression of 60n contains an odd number of 1’s. Find the sum of the squares of the digits of n.

11.
Find the sum of the 7 smallest positive integers n such that n is a multiple of 7, and the repeating decimal expansion of 1/n does not have a period of 6.

12.
Let n be an integer from 1 to 999, inclusive. How many different numerators are possible when n/1000 is written as a common fraction in lowest terms?

13.
How many ways are there to divide a pile of 15 indistinguishable bricks?

14.
Let n be the unique 3-digit positive integer such that the value of the product 100n can be expressed in bases b, b + 1, b + 2, and b + 3 using only 0’s and 1’s, for some integer b > 1. Find n.

15.
For positive integers n, let f(n) be the sum of the positive integer divisors of n. Suppose a positive integer k is untouchable if there does not exist a positive integer a such that f(a) = k + a. For example, the integers 2 and 5 are untouchable, by the above definition. Find the next smallest integer after 2 and 5 that is untouchable.

Answer key:
WARNING: SPOILERS!!!
17 replies
Melissa.
Apr 8, 2025
fake123
5 hours ago
9 Will I make AMO?
imagien_bad   7
N Yesterday at 10:50 PM by alcumusftwgrind
Hi everyone, I got a 100.5 on AMC 12A 2024 what is my chance to make USAMO 2025? (i did not do 12B btw)
7 replies
imagien_bad
Nov 23, 2024
alcumusftwgrind
Yesterday at 10:50 PM
Rutgers Expo in Problem Solving 2025 by OMMC
DottedCaculator   2
N Yesterday at 10:32 PM by Inaaya
Hello to all creative problem solvers,

Do you want a life changing math experience?
Do you want to see me in real life?

Check out the
Rutgers Expo in Problem Solving (REPS) by OMMC!

What is OMMC?

OMMC is presenting to you its next major event: in-person this time! This spring, OMMC is hosting its THIRD IN-PERSON event, where we will be presenting various speakers of math, holding breakout sessions, games and friendly competitions, and providing a math hub for people all over to learn and enjoy. No math experience is needed, and elementary, middle and high schoolers can all register!

The Rutgers Expo in Problem Solving will take place on Saturday, April 19th, 2025, 1 PM Eastern Time.
The venue is the Science Engineering Complex at Rutgers New-Brunswick. This is 96 Frelinghuysen Rd, Piscataway, NJ 08854.


Event includes:

[list]
[*]Math speakers, including university professors
[*]Activities including estimathon and mini math competition WITH PRIZES
[*]Itinerary coming soon!
[/list]

This event is completely FREE to all students!
Fill out the registration form linked below to sign-up for this event and answer some important questions.
https://docs.google.com/forms/d/e/1FAIpQLSeAr2Nul9MBO_adVzHN9Rsrc8yQEjzxPXZHZ-LUFf-zWcwR7A/viewform?usp=preview


Students from anywhere can attend, as long as you can commute to the venue. Email us at ommcofficial@gmail.com for any questions or concerns.

We can’t wait to see you there!
- REPS Team

OMMC’S 2025 EVENTS ARE SPONSORED BY:

[list]
[*]Nontrivial Fellowship
[*]Citadel
[*]Jane Street
[/list]

2 replies
DottedCaculator
Yesterday at 8:46 PM
Inaaya
Yesterday at 10:32 PM
Intro/intermediate books in terms of importance
Aaron_Q   6
N Yesterday at 9:20 PM by Aaron_Q
Hey everyone,
what are your opinions on the most critical (NEED to learn) intro/intermediate books?
i might be cooked
6 replies
Aaron_Q
Tuesday at 11:19 PM
Aaron_Q
Yesterday at 9:20 PM
Some Important Problems in Mathematics
fossasor   11
N Apr 1, 2025 by fossasor
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11 replies
fossasor
Apr 1, 2025
fossasor
Apr 1, 2025
Some Important Problems in Mathematics
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fossasor
549 posts
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Yihangzh
717 posts
#2
Y by
@ above, bruh
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jkim0656
667 posts
#3
Y by
#2 is so sigma
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Yihangzh
717 posts
#4
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jkim0656 wrote:
#2 is so sigma

:dry: :dry: :dry:
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jkim0656
667 posts
#5
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stop postfarming dude
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fossasor
549 posts
#6
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This isn't post farming, it's an April fools joke.
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jkim0656
667 posts
#7
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wait what?
where i live its still 9:23 on 3/31 loll
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yaxuan
3382 posts
#8
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jkim0656 wrote:
wait what?
where i live its still 9:23 on 3/31 loll

In EST, it is midnight on 4/1 already.
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jkim0656
667 posts
#9
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oh$~~~~~$
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fossasor
549 posts
#10
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Shout-out to Zhenghua for being orz (I think I met you as a sevvie lol)
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jkim0656
667 posts
#11
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fossasor wrote:
Shout-out to Zhenghua for being orz (I think I met you as a sevvie lol)

whos Zhenghua?
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fossasor
549 posts
#12
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jkim0656 wrote:
#2 is so sigma

Indeed, it is quite rizzy
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