Here, you will find some general resources, but you may also check out the subheadings for tournament practice exams and cheat sheets.
GAME Topics 2020-21: https://drive.google.com/file/d/1lhGDQrbGvgTa47GFiawRWouEsZU6C3fT/view?usp=sharing
See the below PDFs for the 2021 AMC Questions.
You can find AMC Solutions by searching for the 2021 AMC on artofproblemsolving.com.
AMC 10 A Practice Problems (2021)
AMC 10 B Practice Problems (2021)
AMC 10 B Practice Problems (2021)
AMC 10 B Practice Problems (2021)
From the former captain:
I am often asked, "How can I best prepare for the AMC/AIME competitions?" Here, the AMC (American Math Competition) is the national competition that qualifies you for the next round of the prestigious MAA competition series, the AIME (American Invitational Math Exam). You can learn more about what it is at the top of our AMC sign-up form, https://forms.gle/ns2RAd3gMpYQDePb7, or at https://www.maa.org/math-competitions.
Here's the comprehensive answer to that question, divided by how interested you are:
If you're super serious about preparing, here are a ton of tips:
Solve lots and lots of problems! Competition math is unique in that for the most part, there really isn't a curriculum of things you need to understand persay (it's a lot more about the reasoning and critical thinking skills you develop overtime), and through practices, I strive to explain pretty much everything you need to know in terms of content, which you can augment with the books below. The best way to get a grasp for the kinds of questions that are asked in the AMC and to get better is to practice a lot! I would check out the AMC 10 problem database (https://artofproblemsolving.com/wiki/index.php/AMC_10_Problems_and_Solutions) and the AMC 12 database (https://artofproblemsolving.com/wiki/index.php/AMC_12_Problems_and_Solutions), and there are many more practice sets if you google "AMC practice." Attending other math competitions also helps!
I also know that the MATHCOUNTS Trainer (at https://artofproblemsolving.com/mathcounts_trainer) and For the Win! (at https://artofproblemsolving.com/ftw) are super great game-show-style ways to try your hand at some problems. These are geared more towards AMC 10 in terms of difficulty level.
If you're willing to invest in books, the absolute best books are the Art of Problem Solving book series: Art of Problem Solving Volume 1: The Basics and Art of Problem Solving Volume 2: and Beyond. You'll need to get the solution manuals as well. I would probably start with the first volume and work your way up to the second, but that depends on how confident you feel with competition math already! You could start at Volume 2 if you feel relatively confident with the competition math in middle school and on MATHCOUNTS (if that is something you've done) as that's mostly what Volume 1 covers.
Another book I've found really great is the Three-Year MATHCOUNTS Marathon by Karen Ge. I know that this is geared towards the MATHCOUNTS competition, but the difficulty level of the problems in the book are way above middle school. All the concepts explored in there are super relevant for varsity (and JV) competitions, which relates so well to the AMC, and you can get a lot out of the concise explanations throughout the book. Also, this book focuses mainly on AIME problems than the AMC, so it is a bit further down the road from AMC, but A Gentle Introduction to the American Invitational Mathematics Exam by Scott A. Annin is also a great resource!
If you're super invested in this, the Art of Problem Solving has a lot of online courses specifically tailored to the AMC and AIME series, including a Special AMC Seminar series that lasts for one weekend just before the AMC, so you could check those out as well.
One way I personally really like to study for math competitions is by finding "cheat sheets," essentially documents that compile formulas for you to learn. This is by no means something meant for you to memorize or for you to feel like you have to know all of them (because honestly, you can do really well on the AMC without using any formulas!) but seeing lists of formulas and trying to figure out how they were derived and what they would be used for helps you see the swath of potential concepts in math tournaments and learn how they all fit together. My favorite at the moment is Eashan Gandotra's Formulas for Pre-Olympiad Math, but I also like Coach Monk's High School Playbook and the outline All of Math in Three Pages. You can find all of these links in the Cheat Sheets tab below Resources. Again, these are not for you to memorize but to give you a reference sheet as you pick up concepts in contest math and to give you something to review before a competition. It really helps me get in the mindset before taking a math competition to review one of these sheets, so that's something unique I've picked up over the years.
If you just have a bit of time and aren't overly invested, but you still want to prepare:
Solve some problems! Take at least one or two practice tests on https://artofproblemsolving.com/wiki/index.php/AMC_10_Problems_and_Solutions or https://artofproblemsolving.com/wiki/index.php/AMC_12_Problems_and_Solutions. Remember that a very good score does not require solving that many problems on the exam, and practicing helps you hone your skills to get the score you want!
Check out a list of topics and formulas through Eashan Gandotra's Formulas for Pre-Olympiad Math in the Cheat Sheets tab. Do not feel like you need to know all of them (you don't!) but review and remember at least the beginning ones in each section and remind yourself of what you do know before the exam.
Come to math team practices! We are working our way through an AMC 12 Seminar at the moment, covering the four general competition topics, Algebra, Geometry, Number Theory and Combinatorics, so that should be very helpful in preparing.
I hope this helps!