Subcategories

• M0 Introduction

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  In the video, Prof. Loh explains how to find the middle number (9) by using algebra. But apparently, my brain wasn't satisfied with that method, so I accidentally possibly came up with a shortcut... maybe. Here's how I did it: I simply found the median of the 9 numbers, which was also 9. It actually kinda makes sense because in previous problems, the middle number was always the median of the numbers given. But I also know that there are often weird coincidences in math, (when you get the right answer the wrong way) so that's why I'm asking this wonderful math community 🙂

• M1 Algebra Basics

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  Hi, just have a quick question here, which is not totally about this challenge explanation but does concern repeating decimals. Once at my school, we solved an equation with the result being a repeating decimal: 0.016 (the 6 being repeated). There was a little confusion about how to say it in word form, as we were told to use "and" instead of "point" to refer to the decimal point. For example: "zero and 16 thousandths repeating". But doesn't that sound like the whole 16 is repeating (.0161616...)? So please if possible let us/me know what you think it should be. Help is appreciated!
  Thank you!

• M2 Geometry Tools

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  Hi! This is in relation the question at the end of this explanation. I'm confused about how angle CGH can be inscribed to arc CG. Could someone help explain? Thank you 🙂

• M3 Combinatorics Tools

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  In the video, when Prof. Loh was explaining the second way to do the pirates and gold coins problem, he only took away 8 choose 3. I thought you should take away all the different cases like 7 choose 3, 6 choose 3, etc. Why didn't he take away the rest? Thanks.

• M4 Algebra Tools

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  For this problem a solution that could possibly be used is using divisibility rules. Note how 117 is a multiple of 9 which automatically means that and number that 117 multiplies (in this case 113) Has to be a multiple of 9 as well. Note then how only i.) is a multiple of 9 out of all three solutions, therefore the only possible solution.

• M5 Number Theory Tools

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  Man this is too hard to understand

• Practice Mini-Courses

  Workout 1A (Algebra) Workout 1B (Algebra) Workout 2A (Geometry) Workout 2B (Geometry) Workout 3A (Combinatorics) Workout 4A (Algebra) Workout 5A (Number Theory)
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  Since 2021=2025-4=45^2-2^2, which means that 2021 can be written as (45+2)(45-2)=43*47. It's more faster than guessing the numbers and it's more easy to memorize. Although not all numbers can be solved that way